freebsd-skq/sbin/vinum/vinum.8

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.Dd 28 March 1999
.Dt vinum 8
.Sh NAME
.Nm vinum
.Nd Logical Volume Manager control program
.Sh SYNOPSIS
.Nm
.Op command
.Op Fl options
.Sh COMMANDS
.Cd create Op Fl f Ar description-file
.in +1i
Create a volume as described in
.Ar description-file
.in
.\" XXX remove this
.Cd attach Ar plex Ar volume
.Op Nm rename
.Cd attach Ar subdisk Ar plex Ar [offset]
.Op Nm rename
.in +1i
Attach a plex to a volume, or a subdisk to a plex.
.in
.\" XXX remove this
.Cd debug
.in +1i
Cause the volume manager to enter the kernel debugger.
.in
.Cd debug
.Ar flags
.in +1i
Set debugging flags.
.in
.Cd detach
.Op Ar plex | subdisk
.in +1i
Detach a plex or subdisk from the volume or plex to which it is attached.
.in
.Cd info
.Op Fl v
.in +1i
List information about volume manager state.
.in
.Cd init
.Op Fl v
.Op Fl w
.Ar plex
.in +1i
.\" XXX
Initialize a plex by writing zeroes to all its subdisks.
.in
.Cd label
.Ar volume
.in +1i
Create a volume label
.in
.Cd list
.Op Fl r
.Op Fl s
.Op Fl v
.Op Fl V
.Op volume | plex | subdisk
.in +1i
List information about specified objects
.in
.Cd l
.Op Fl r
.Op Fl s
.Op Fl v
.Op Fl V
.Op volume | plex | subdisk
.in +1i
List information about specified objects (alternative to
.Cd list
command)
.in
.Cd ld
.Op Fl r
.Op Fl s
.Op Fl v
.Op Fl V
.Op volume
.in +1i
List information about drives
.in
.Cd ls
.Op Fl r
.Op Fl s
.Op Fl v
.Op Fl V
.Op subdisk
.in +1i
List information about subdisks
.in
.Cd lp
.Op Fl r
.Op Fl s
.Op Fl v
.Op Fl V
.Op plex
.in +1i
List information about plexes
.in
.Cd lv
.Op Fl r
.Op Fl s
.Op Fl v
.Op Fl V
.Op volume
.in +1i
List information about volumes
.in
.Cd printconfig
.Op Pa file
.in +1i
Write a copy of the current configuration to
.Pa file .
.in
.Cd makedev
.in +1i
Remake the device nodes in
.Ar /dev/vinum .
.in
.Cd quit
.in +1i
Exit the
.Nm
program when running in interactive mode.  Normally this would be done by
entering the
.Ar EOF
character.
.in
.Cd read
.Ar disk Op disk...
.in +1i
Read the
.Nm
configuration from the specified disks.
.in
.Cd rename Op Fl r
.Ar [ drive | subdisk | plex | volume ]
.Ar newname
.in +1i
Change the name of the specified object.
.ig
XXX
.in
.Cd replace
.Ar [ subdisk | plex ]
.Ar newobject
.in +1i
Replace the object with an identical other object.  XXX not implemented yet.
..
.in
.Cd resetconfig
.in +1i
Reset the complete
.Nm
configuration.
.in
.Cd resetstats
.Op Fl r
.Op volume | plex | subdisk
.in +1i
Reset statistisc counters for the specified objects, or for all objects if none
are specified.
.in
.Cd rm
.Op Fl f
.Op Fl r
.Ar volume | plex | subdisk
.in +1i
Remove an object
.in
.Cd saveconfig
.in +1i
Save
.Nm
configuration to disk.
.in
.ig
XXX
.Cd set
.Op Fl f
.Ar state
.Ar volume | plex | subdisk | disk
.in +1i
Set the state of the object to \fIstate\fP\|
.in
..
.Cd setdaemon
.Op value
.in +1i
Set d<>mon configuration.
.in
.Cd start
.in +1i
Read configuration from all vinum drives.
.in
.Cd start
.Op volume | plex | subdisk
.in +1i
Allow the system to access the objects
.in
.Cd stop
.Op Fl f
.Op volume | plex | subdisk
.in +1i
Terminate access to the objects, or stop
.Nm
if no parameters are specified.
.in
.Sh DESCRIPTION
.Nm
is a utility program to communicate with the \fBVinum\fP\| logical volume
manager.  See
.Xr vinum 4
for more information about the volume manager.
.Xr vinum 8
is designed either for interactive use, when started without a command, or to
execute a single command if the command is supplied as arguments to
.Nm vinum .
In interactive mode,
.Nm
maintains a command line history.
.Ss OPTIONS
.Nm
commands may optionally be followed by an option.  Any of the following options
may be specified with any command, but in some cases they do not make any
difference: cases, the options are ignored.  For example, the
.Nm stop
command ignores the
.Fl v
and
.Fl V
options.
.Bl -hang
.It Fl f
The
.Fl f
.if t (``force'')
.if n ("force")
option overrides safety checks.  Use with extreme care.  This option is for
emergency use only.  For example, the command
.Bd -unfilled -offset indent
rm -f myvolume
.Ed
.Pp
removes
.Ar myvolume
even if it is open.  Any subsequent access to the volume will almost certainly
cause a panic.
.It Fl r
The
.Fl r
.if t (``recursive'')
.if n ("recursive")
option is used by the list commands to display information not
only about the specified objects, but also about subordinate objects.  For
example, in conjnction with the
.Nm lv
command, the
.Fl r
option will also show information about the plexes and subdisks belonging to the
volume.
.It Fl s
The
.Fl s
.if t (``statistics'')
.if n ("statistics")
option is used by the list commands to display statistical information.
.It Fl v
The
.Fl v
.if t (``verbose'')
.if n ("verbose")
option can be used with any command to request more detailed information.
.It Fl V
The
.Fl V
.if t (``Very verbose'')
.if n ("Very verbose")
option can be used with any command to request more detailed information than
the
.Fl v
option provides.
.It Fl w
The
.Fl w
.if t (``wait'')
.if n ("wait")
option tells
.Nm
to wait for completion of commands which normally run in the background, such as
.Nm init .
.El
.Pp
.Ss COMMANDS IN DETAIL
.Pp
.Nm
commands perform the following functions:
.Bl -hang
.It Nm attach Ar plex Ar volume
.Op Nm rename
.if n .sp -1v
.if t .sp -.6v
.It Nm attach Ar subdisk Ar plex Ar [offset]
.Op Nm rename
.sp
.Nm
.Ar attach
inserts the specified plex or subdisk in a volume or plex.  In the case of a
subdisk, an offset in the plex may be specified.  If it is not, the subdisk will
be attached at the first possible location.  After attaching a plex to a
non-empty volume,
.Nm
reintegrates the plex.
.Pp
If the keyword
.Nm rename
is specified,
.Nm
renames the object (and in the case of a plex, any subordinate subdisks) to fit
in with the default
.Nm
naming convention.
.Pp
A number of considerations apply to attaching subdisks:
.Bl -bullet
.It
Subdisks can normally only be attached to concatenated plexes.
.It
If a striped or RAID-5 plex is missing a subdisk (for example after drive
failure), it may be replaced by a subdisk of the same size only.  No other
attachment of subdisks is currently allowed.
.It
For concatenated plexes, the
.Ar offset
parameter specifies the offset in blocks from the beginning of the plex.  For
striped and RAID-5 plexes, it specifies the offset of the first block of the
subdisk: in other words, the offset is the numerical position of the subdisk
multiplied by the stripe size.  For example, in a plex of block size 256k, the
first subdisk will have offset 0, the second offset 256k, the third 512k, etc.
This calculation ignores parity blocks in RAID-5 plexes.
.El
.It Nm create Op Fl f Ar description-file
.sp
.Nm
.Ar create
is used to create any object.  In view of the relatively complicated
relationship and the potential dangers involved in creating a
.Nm
object, there is no interactive interface to this function.  If you do not
specify a file name,
.Nm
starts an editor on a temporary file.  If the environment variable
.Ev EDITOR
is set,
.Nm
starts this editor.  If not, it defaults to
.Nm vi .
See the section CONFIGURATION FILE below for more information on the format of
this file.
.Pp
Note that the
.Nm
.Ar create
function is additive: if you run it multiple times, you will create multiple
copies of all unnamed objects.
.Pp
Normally the
.Nm create
command will not change the names of existing
.Nm
drives, in order to avoid accidentally erasing them.  The correct way to dispose
of no longer wanted
.Nm
drives is to reset the configuration with the
.Nm resetconfig
command.  In some cases, however, it may be necessary to create new data on
.Nm
drives which can no longer be started.  In this case, use the
.Nm create Fl f
command.
.It Nm debug
.Pp
.Nm
.Ar debug
is used to enter the remote kernel debugger.  It is only activated if
.Nm
is built with the
.Ar VINUMDEBUG
option.  This option will stop the execution of the operating system until the
kernel debugger is exited.  If remote debugging is set and there is no remote
connection for a kernel debugger, it will be necessary to reset the system and
reboot in order to leave the debugger.
.It Nm debug
.Ar flags
.Pp
Set a bit mask of internal debugging flags.  These will change without warning
as the product matures; to be certain, read the header file
.Pa sys/dev/vinumvar.h .
The bit mask is composed of the following values:
.Bl -hang
.It DEBUG_ADDRESSES (1)
.br
Show buffer information during requests
.It DEBUG_NUMOUTPUT (2)
.br
Show the value of
.Dv vp->v_numoutput.
.It DEBUG_RESID (4)
.br
Go into debugger in
.Fd complete_rqe.
.It DEBUG_LASTREQS (8)
.br
Keep a circular buffer of last requests.
.It DEBUG_REVIVECONFLICT (16)
.br
Print info about revive conflicts.
.It DEBUG_EOFINFO (32)
.br
Print information about internal state when returning an EOF on a striped plex.
.It DEBUG_MEMFREE (64)
.br
Maintain a circular list of the last memory areas freed by the memory allocator.
.It DEBUG_REMOTEGDB (256)
.br
Go into remote
.Ic gdb
when the
.Nm debug
command is issued.
.It DEBUG_WARNINGS (512)
.br
Print some warnings about minor problems in the implementation.
.El
.It Nm detach Op Fl f
.Ar plex
.if n .sp -1v
.if t .sp -.6v
.It Nm detach Op Fl f
.Ar subdisk
.sp
.Nm
.Ar detach
removes the specified plex or subdisk from the volume or plex to which it is
attached.  If removing the object would impair the data integrity of the volume,
the operation will fail unless the
.Fl f
option is specified.  If the object is named after the object above it (for
example, subdisk vol1.p7.s0 attached to plex vol1.p7), the name will be changed
by prepending the text 
.if t ``ex-'' 
.if n "ex-" 
(for example, ex-vol1.p7.s0).  If necessary, the name will be truncated in the
process.
.Pp
.Nm detach
does not reduce the number of subdisks in a striped or RAID-5 plex.  Instead,
the subdisk is marked absent, and can later be replaced with the
.Nm attach
command.
.It Nm info
.br
.Nm
.Ar info
displays information about
.Nm
memory usage.  This is intended primarily for debugging.  With the
.Fl v
option, it will give detailed information about the memory areas in use.
.Pp
With the
.Fl V
option,
.Ar info
displays information about the last up to 64 I/O requests handled by the
.Nm
driver.  This information is only collected if debug flag 8 is set.  The format
looks like:
.Pp
.Bd -literal
vinum -> info -V
Flags: 0x200    1 opens
Total of 38 blocks malloced, total memory: 16460
Maximum allocs:       56, malloc table at 0xf0f72dbc

Time             Event       Buf        Dev     Offset          Bytes   SD      SDoff   Doffset Goffset

14:40:00.637758 1VS Write 0xf2361f40    0x5b03  0x10            16384
14:40:00.639280 2LR Write 0xf2361f40    0x5b03  0x10            16384
14:40:00.639294 3RQ Read  0xf2361f40    0x427   0x104109        8192    19      0       0       0
14:40:00.639455 3RQ Read  0xf2361f40    0x417   0xd2109         8192    17      0       0       0
14:40:00.639529 3RQ Read  0xf2361f40    0x40f   0x6e109         8192    16      0       0       0
14:40:00.652978 4DN Read  0xf2361f40    0x427   0x104109        8192    19      0       0       0
14:40:00.667040 4DN Read  0xf2361f40    0x40f   0x6e109         8192    16      0       0       0
14:40:00.668556 4DN Read  0xf2361f40    0x417   0xd2109         8192    17      0       0       0
14:40:00.669777 6RP Write 0xf2361f40    0x427   0x104109        8192    19      0       0       0
14:40:00.685547 4DN Write 0xf2361f40    0x427   0x104109        8192    19      0       0       0
.Ed
.Pp
The
.Ar Buf
field always contains the address of the user buffer header.  This can be used
to identify the requests associated with a user request, though this is not 100%
reliable: theoretically two requests in sequence could use the same buffer
header, though this is not common.  The beginning of a request can be identified
by the event
.Ar 1VS .
The example above shows the requests involved in a single user request.
.Pp
The
.Ar Event
field contains information related to the sequence of events in the request
chain.  The digit
.Ar 1
to
.Ar 6
indicates the approximate sequence of events, and the two-letter abbreviation is
a mnemonic for the location
.Bl -hang
.It 1VS
(vinumstrategy) shows information about the user request on entry to
.Fd vinumstrategy .
The device number is the
.Nm
device, and offset and length are the user parameters.  This is always the
beginning of a request sequence.
.It 2LR
(launch_requests) shows the user request just prior to launching the low-level
.Nm
requests in the function
.Fd launch_requests.
The parameters should be the same as in the
.Ar 1VS
information.
.Pp
In the following requests,
.Ar Dev
is the device number of the associated disk partition,
.Ar Offset
is the offset from the beginning of the partition,
.Ar SD
is the subdisk index in
.Dv vinum_conf ,
.Ar SDoff
is the offset from the beginning of the subdisk,
.Ar Doffset
is the offset of the associated data request, and
.Ar Goffset
is the offset of the associated group request, where applicable.
.It 3RQ
(request) shows one of possibly several low-level
.Nm
requests which are launched to satisfy the high-level request.  This information
is also logged in
.Fd launch_requests.
.It 4DN
(done) is called from
.Fd complete_rqe,
showing the completion of a request.  This completion should match a request
launched either at stage
.Ar 4DN
from
.Fd launch_requests,
or from
.Fd complete_raid5_write
at stage
.Ar 5RD
or
.Ar 6RP .
.It 5RD
(RAID-5 data) is called from
.Fd complete_raid5_write
and represents the data written to a RAID-5 data stripe after calculating
parity.
.It 6RP
(RAID-5 parity) is called from
.Fd complete_raid5_write
and represents the data written to a RAID-5 parity stripe after calculating
parity.
.El
.\" XXX
.It Nm init Op Fl w
.Ar plex
.Pp
.Nm
.Ar init
initializes a plex by writing zeroes to all its subdisks.  This is the only way
to ensure consistent data in a plex.  You must perform this initialization
before using a RAID-5 plex.  It is also recommended for other new plexes.
.Nm
initializes all subdisks of a plex in parallel.  Since this operation can take a
long time, it is normally performed in the background.  If you want to wait for
completion of the command, use the
.Fl w
(wait) option.
.Nm
prints a console message when the initialization is complete.
.It Nm label
.Ar volume
.Pp
The
.Nm label
command writes a
.Ar ufs
style volume label on a volume.  It is a simple alternative to an appropriate
call to
.Ar disklabel .
This is needed because some
.Ar ufs
commands still read the disk to find the label instead of using the correct
.Ar ioctl
call to access it.
.Nm
maintains a volume label separately from the volume data, so this command is not
needed for
.Ar newfs .
This command is deprecated.
.Pp
.It Nm list
.Op Fl r
.Op Fl V
.Op volume | plex | subdisk
.if n .sp -1v
.if t .sp -.6v
.It Nm l
.Op Fl r
.Op Fl V
.Op volume | plex | subdisk
.if n .sp -1v
.if t .sp -.6v
.It Nm ld
.Op Fl r
.Op Fl s
.Op Fl v
.Op Fl V
.Op volume
.if n .sp -1v
.if t .sp -.6v
.It Nm ls
.Op Fl r
.Op Fl s
.Op Fl v
.Op Fl V
.Op subdisk
.if n .sp -1v
.if t .sp -.6v
.It Nm lp
.Op Fl r
.Op Fl s
.Op Fl v
.Op Fl V
.Op plex
.if n .sp -1v
.if t .sp -.6v
.It Nm lv
.Op Fl r
.Op Fl s
.Op Fl v
.Op Fl V
.Op volume
.Pp
.Ar list
is used to show information about the specified object.  If the argument is
omitted, information is shown about all objects known to
.Nm vinum .
The
.Ar l
command is a synonym for
.Ar list .
.Pp
The
.Fl r
option relates to volumes and plexes: if specified, it recursively lists
information for the subdisks and (for a volume) plexes subordinate to the
objects.  The commands
.Ar lv ,
.Ar lp ,
.Ar ls
and
.Ar ld
commands list only volumes, plexes, subdisks and drives respectively.  This is
particularly useful when used without parameters.
.Pp
The
.Fl s
option causes
.Nm
to output device statistics, the
.Op Fl v
(verbose) option causes some additional information to be output, and the
.Op Fl V
causes considerable additional information to be output.
.It Nm makedev
.br
The
.Nm makedev
command removes the directory /dev/vinum and recreates it with device nodes
which reflect the current configuration.  This command is not intended for
general use, and is provided for emergency use only.
.Pp
.It Nm quit
Exit the
.Nm
program when running in interactive mode.  Normally this would be done by
entering the
.Ar EOF
character.
.It Nm printconfig Op Pa file
Write a copy of the current configuration to
.Pa file
in a format that can be used to recreate the
.Nm
configuration.  Unlike the configuration saved on disk, it includes definitions
of the drives.  If you omit
.Pa file ,
.Nm
writes the list to
.Pa stdout .
.It Nm read
.Ar disk Op disk...
.Pp
The
.Nm read
command scans the specified disks for
.Nm
partitions containing previously created configuration information.  It reads
the configuration in order from the most recently updated to least recently
updated configuration.
.Nm
maintains an up-to-date copy of all configuration information on each disk
partition.  You must specify all of the slices in a configuration as the
parameter to this command.
.Pp
The
.Nm read
command is intended to selectively load a
.Nm
configuration on a system which has other
.Nm
partitions.  If you want to start all partitions on the system, it is easier to
use the
.Nm start
command.
.Pp
If
.Nm
encounters any errors during this command, it will turn off automatic
configuration update to avoid corrupting the copies on disk.  This will also
happen if the configuration on disk indicates a configuration error (for
example, subdisks which do not have a valid space specification).  You can turn
the updates on again with the
.Nm setdaemon
and
.Nm saveconfig
commands.  Reset bit 4 of the daemon options mask to re-enable configuration
saves.
.It Nm rename
.Op Fl r
.Ar [ drive | subdisk | plex | volume ]
.Ar newname
.Pp
Change the name of the specified object.  If the
.Fl r
option is specified, subordinate objects will be named by the default rules:
plex names will be formed by appending .p\f(BInumber\fP to the volume name, and
subdisk names will be formed by appending .s\f(BInumber\fP to the plex name.
.It Nm replace
.Ar [ subdisk | plex ]
.Ar newobject
.Pp
Replace the object with an identical other object.  This command has not yet
been implemented.
.It Nm resetconfig
.Pp
The
.Nm resetconfig
command completely obliterates the
.Nm
configuration on a system.  Use this command only when you want to completely
delete the configuration.
.Nm
will ask for confirmation: you must type in the words NO FUTURE exactly
as shown:
.Bd -unfilled -offset indent
# \f(CBvinum resetconfig\f(CW

WARNING!  This command will completely wipe out your vinum
configuration.  All data will be lost.  If you really want
to do this, enter the text

NO FUTURE
Enter text -> \f(BINO FUTURE\fP
Vinum configuration obliterated
.Ed
.ft R
.Pp
As the message suggests, this is a last-ditch command.  Don't use it unless you
have an existing configuration which you never want to see again.
.It Nm resetstats
.Op Fl r
.Op volume | plex | subdisk
.Pp
.Nm
maintains a number of statistical counters for each object.  See the header file
.Fi vinumvar.h
for more information.
.\" XXX put it in here when it's finalized
Use the
.Nm resetstats
command to reset these counters.  In conjunction with the
.Fl r
option,
.Nm
also resets the counters of subordinate objects.
.It Nm rm
.Op Fl f
.Op Fl r
.Ar volume | plex | subdisk
.Pp
.Nm rm
removes an object from the
.Nm
configuration.  Once an object has been removed, there is no way to recover it.
Normally
.Nm
performs a large amount of consistency checking before removing an object.  The
.Fl f
option tells
.Nm
to omit this checking and remove the object anyway.  Use this option with great
care: it can result in total loss of data on a volume.
.Pp
Normally,
.Nm
refuses to remove a volume or plex if it has subordinate plexes or subdisks
respectively.  You can tell
.Nm
to remove the object anyway by using the
.Fl f
flag, or you can cause
.Nm
to remove the subordinate objects as well by using the
.Fl r
(recursive) flag.  If you remove a volume with the
.Fl r
flag, it will remove both the plexes and the subdisks which belong to the
plexes.
.It Nm saveconfig
.Pp
Save the current configuration to disk.  This is primarily a maintenance
function.  For example, if an error occurs on startup, updates will be
disabled.  When you reenable them, the configuration is not automatically saved
to disk.  Use this command to save the configuration.
.ig
.It Nm set
.Op Fl f
.Ar state
.Ar volume | plex | subdisk | disk
.Nm set
sets the state of the specified object to one of the valid states (see OBJECT
STATES below).  Normally
.Nm
performs a large amount of consistency checking before making the change.  The
.Fl f
option tells
.Nm
to omit this checking and perform the change anyway.  Use this option with great
care: it can result in total loss of data on a volume.
.\"XXX
.Nm This command has not yet been implemented.
..
.It Nm setdaemon
.Op value
.Pp
.Nm setdaemon
sets a variable bitmask for the
.Nm
d<EFBFBD>mon.  This command is temporary and will be replaced.  Currently, the bit mask
may contain the bits 1 (log every action to syslog) and 4 (don't update
configuration).  Option bit 4 can be useful for error recovery.
.It Nm start
.Op volume | plex | subdisk
.Pp
.Nm start
starts (brings into to the
.Ar up
state) one or more
.Nm
objects.
.Pp
If no object names are specified,
.Nm
scans the disks known to the system for
.Nm
drives and then reads in the configuration as described under the
.Nm read
commands.  The
.Nm
drive contains a header with all information about the data stored on the drive,
including the names of the other drives which are required in order to represent
plexes and volumes.
.Pp
If
.Nm
encounters any errors during this command, it will turn off automatic
configuration update to avoid corrupting the copies on disk.  This will also
happen if the configuration on disk indicates a configuration error (for
example, subdisks which do not have a valid space specification).  You can turn
the updates on again with the
.Nm setdaemon
and
.Nm saveconfig
command.  Reset bit 4 of the daemon options mask to re-enable configuration
saves.
.Pp
If object names are specified,
.Nm
starts them.  Normally this operation is only of use with subdisks.  The action
depends on the current state of the object:
.Bl -bullet
.It
If the
object is already in the
.Ar up
state,
.Nm
does nothing.
.It
If the object is a subdisk in the
.Ar down
or
.Ar reborn
states,
.Nm
changes it to the
.Ar up
state.
.It
If the object is a subdisk in the
.Ar empty
state, the change depends on the subdisk.  If it is part of a plex which is part
of a volume which contains other plexes,
.Nm
places the subdisk in the
.Ar reviving
state and attempts to copy the data from the volume.  When the operation
completes, the subdisk is set into the
.Ar up
state.  If it is part of a plex which is part of a volume which contains no
other plexes, or if it is not part of a plex,
.Nm
brings it into the
.Ar up
state immediately.
.It
If the object is a subdisk in the
.Ar reviving
state,
.Nm
continues the
.Ar revive
operation offline.  When the operation completes, the subdisk is set into the
.Ar up
state.
.El
.Pp
When a subdisk comes into the
.Ar up
state,
.Nm
automatically checks the state of any plex and volume to which it may belong and
changes their state where appropriate.
.Pp
If the object is a volume or a plex,
.Nm start
currently has no effect: it checks the state of the subordinate subdisks (and
plexes in the case of a volume) and sets the state of the object accordingly.
In a later version, this operation will cause the subdisks
.Pp
To start a plex in a multi-plex volume, the data must be copied from another
plex in the volume.  Since this frequently takes a long time, it is done in the
background.
.It Nm stop
.Op Fl f
.Op volume | plex | subdisk
.Pp
If no parameters are specified,
.Nm stop
removes the
.Nm
kld and stops
.Xr vinum 8 .
This can only be done if no objects are active, In particular, the
.Fl f
flag does not override this requirement.  This command can only work if
.Nm
has been loaded as a kld, since it is not possible to unload a statically
configured driver.
.Nm
.Nm stop
will fail if
.Nm
is statically configured.
.Pp
If object names are specified,
.Nm stop
disables access to the objects.  If the objects have  subordinate objects, they
subordinate objects must either already be inactive (stopped or in error), or
the
.Fl r
and
.Fl f
flags must be specified.  This command does not remove the objects from the
configuration.  They can be accessed again after a
.Nm start
command.
.Pp
By default,
.Nm
does not stop active objects.  For example, you cannot stop a plex which is
attached to an active volume, and you cannot stop a volume which is open.  The
.Fl f
option tells
.Nm
to omit this checking and remove the object anyway.  Use this option with great
care and understanding: used incorrectly, it can result in serious data
corruption.
.El
.Ss CONFIGURATION FILE
.Nm
requires that all parameters to the
.Nm create
commands must be in a configuration file.  Entries in the configuration file
define volumes, plexes and subdisks, and may be in free format, except that each
entry must be on a single line.
.Pp
Some configuration file parameters specify a size (lengths, stripe sizes).
These lengths can be specified as bytes, as sectors of 512 bytes (by appending
the letter \f(CWs\fR), as kilobytes (by appending the letter \f(CWk\fR), as
megabytes (by appending the letter \f(CWm\fR) or as gigabytes (by appending the
letter \f(CWg\fR).  These quantities represent the values 2**10, 2**20 and 2**30
respectively.  For example, the value \f(CW16777216\fR bytes can also be written
as \f(CW16m\fR, \f(CW16384k\fR or \f(CW32768b\fR.
.Pp
For reasons of compatibility, 
.Nm
takes the letter \f(CWb\fP (block) to be equivalent to \f(CWs\fP (sector).  The
use of this abbreviation is deprecated, since the size of a block is very
dependent on the context.
.Pp
The configuration file can contain the following entries:
.Pp
.Bl -hang -width 4n
.It Nm volume
.Ar name
.Op options
.Pp
Define a volume with name
.Ar name .
.Pp
Options are:
.Pp
.Bl -hang -width 18n
.It Nm plex Ar plexname
Add the specified plex to the volume.  If
.Ar plexname
is specified as
.Ar * ,
.Nm
will look for the definition of the plex as the next possible entry in the
configuration file after the definition of the volume.
.It Nm readpol Ar policy
Define a
.Ar read policy
for the volume.
.Ar policy
may be either
.Nm round
or
.Nm prefer Ar plexname .
.Nm
satisfies a read request from only one of the plexes.  A
.Ar round
read policy specifies that each read should be performed from a different plex
in \fIround-robin\fR\| fashion.  A
.Ar prefer
read policy reads from the specified plex every time.
.It Nm setupstate
.Pp
When creating a multi-plex volume, assume that the contents of all the plexes
are consistent.  This is normally not the case, and correctly you should use the
.Nm init
command to first bring them to a consistent state.  In the case of striped and
concatenated plexes, however, it does not normally cause problems to leave them
inconsistent: when using a volume for a file system or a swap partition, the
previous contents of the disks are not of interest, so they may be ignored.
If you want to take this risk, use this keyword.  It will only apply to the
plexes defined immediately after the volume in the configuration file.  If you
add plexes to a volume at a later time, you must integrate them.
.Pp
Note that you \fImust\fP\| use the
.Nm init
command with RAID-5 plexes: otherwise extreme data corruption will result if one
subdisk fails.
.fi
.El
.It Nm plex Op options
.Pp
Define a plex.  Unlike a volume, a plex does not need a name.  The options may
be:
.Pp
.Bl -hang -width 18n
.It Nm name Ar plexname
Specify the name of the plex.  Note that you must use the keyword
.Ar name
when naming a plex or subdisk.
.sp
.It Nm org Ar organization Op stripesize
.Pp
Specify the organization of the plex.
.Ar organization
can be one of
.Ar concat ,
.Ar striped
or
.Ar raid5 .
For
.Ar striped
and
.Ar raid5
plexes, the parameter
.Ar stripesize
must be specified, while for
.Ar concat
it must be omitted.  For type
.Ar striped ,
it specifies the width of each stripe.  For type
.Ar raid5 ,
it specifies the size of a group.  A group is a portion of a plex which
stores the parity bits all in the same subdisk.   It must be a factor of the plex size (in
other words, the result of dividing the plex size by the stripe size must be an
integer), and it must be a multiple of a disk sector (512 bytes).
.sp
For optimum performance, stripes should be at least 128 kB in size: anything
smaller will result in a significant increase in I/O activity due to mapping of
individual requests over multiple disks.  The performance improvement due to the
increased number of concurrent transfers caused by this mapping will not make up
for the performance drop due to the increase in latency.  A good guideline for
stripe size is between 256 kB and 512 kB.
.Pp
A striped plex must have at least two subdisks (otherwise it is a concatenated
plex), and each must be the same size.  A RAID-5 plex must have at least three
subdisks, and each must be the same size.  In practice, a RAID-5 plex should
have at least 5 subdisks.
.Pp
.It Nm volume Ar volname
Add the plex to the specified volume.  If no
.Nm volume
keyword is specified, the plex will be added to the last volume mentioned in the
configuration file.
.sp
.It Nm sd Ar sdname Ar offset
Add the specified subdisk to the  plex at offset
.Ar offset .
.br
.fi
.El
.It Nm subdisk Op options
.Pp
Define a subdisk.  Options may be:
.Pp
.Bl -hang -width 18n
.nf
.sp
.It Nm name Ar name
Specify the name of a subdisk.  It is not necessary to specify a name for a
subdisk\(emsee OBJECT NAMING above.  Note that you must specify the keyword
.Ar name
if you wish to name a subdisk.
.sp
.It Nm plexoffset Ar offset
Specify the starting offset of the subdisk in the plex.  If not specified,
.Nm
allocates the space immediately after the previous subdisk, if any, or otherwise
at the beginning of the plex.
.sp
.It Nm driveoffset Ar offset
Specify the starting offset of the subdisk in the drive.  If not specified,
.Nm
allocates the first contiguous
.Ar length
bytes of free space on the drive.
.sp
.It Nm length Ar length
Specify the length of the subdisk.  This keyword must be specified.  There is no
default, but the value 0 may be specified to mean 
.if t ``use the largest available contiguous free area on the drive''. 
.if n "use the largest available contiguous free area on the drive". 
If the drive is empty, this means that the entire drive will be used for the
subdisk.
.Nm length
may be shortened to
.Nm len .
.sp
.It Nm plex Ar plex
Specify the plex to which the subdisk belongs.  By default, the subdisk belongs
to the last plex specified.
.sp
.It Nm drive Ar drive
Specify the drive on which the subdisk resides.  By default, the subdisk resides
on the last drive specified.
.br
.fi
.El
.It Nm drive Ar name Op options
.Pp
Define a drive.  The option must be:
.Pp
.Bl -hang -width 18n
.It Nm device Ar devicename
Specify the device on which the drive resides.
.El
.El
.Sh EXAMPLE CONFIGURATION FILE
.Bd -literal
# Sample vinum configuration file
#
# Our drives
drive drive1 device /dev/da1h
drive drive2 device /dev/da2h
drive drive3 device /dev/da3h
drive drive4 device /dev/da4h
drive drive5 device /dev/da5h
drive drive6 device /dev/da6h
# A volume with one striped plex
volume tinyvol
 plex org striped 512b
  sd length 64m drive drive2
  sd length 64m drive drive4
volume stripe
 plex org striped 512b
  sd length 512m drive drive2
  sd length 512m drive drive4
# Two plexes
volume concat
 plex org concat
  sd length 100m drive drive2
  sd length 50m drive drive4
 plex org concat
  sd length 150m drive drive4
# A volume with one striped plex and one concatenated plex
volume strcon
 plex org striped 512b
  sd length 100m drive drive2
  sd length 100m drive drive4
 plex org concat
  sd length 150m drive drive2
  sd length 50m drive drive4
# a volume with a  RAID-5 and a striped plex
# note that the RAID-5 volume is longer by
# the length of one subdisk
volume vol5
 plex org striped 64k
  sd length 1000m drive drive2
  sd length 1000m drive drive4
 plex org raid5 32k
  sd length 500m drive drive1
  sd length 500m drive drive2
  sd length 500m drive drive3
  sd length 500m drive drive4
  sd length 500m drive drive5
.Ed
.Ss DRIVE LAYOUT CONSIDERATIONS
.Nm
drives are currently BSD disk partitions.  They must be of type
.Ar vinum
in order to avoid overwriting file systems.  For compatibility reasons,
.Nm
currently accepts partitions of type
.Ar unused ,
but the next release will not allow this kind of partition.
.Nm
prints a warning message when reading a configuration from a partition of type
.Ar unused .
Use
.Nm disklabel
.Ar -e
to edit a partition type definition.  The following display shows a typical
partition layout as shown by
.Nm disklabel:
.Bd -literal
8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  a:    81920   344064    4.2BSD        0     0     0   # (Cyl.  240*- 297*)
  b:   262144    81920      swap                        # (Cyl.   57*- 240*)
  c:  4226725        0    unused        0     0         # (Cyl.    0 - 2955*)
  e:    81920        0    4.2BSD        0     0     0   # (Cyl.    0 - 57*)
  f:  1900000   425984    4.2BSD        0     0     0   # (Cyl.  297*- 1626*)
  g:  1900741  2325984     vinum        0     0     0   # (Cyl. 1626*- 2955*)
.Ed
.sp
In this example, partition
.Nm g
may be used as a
.Nm
partition.  Partitions
.Nm a ,
.Nm e
and
.Nm f
may be used as
.Nm UFS
file systems or
.Nm ccd
partitions.  Partition
.Nm b
is a swap partition, and partition
.Nm c
represents the whole disk and should not be used for any other purpose.
.Pp
.Nm
uses the first 265 sectors on each partition for configuration information, so
the maximum size of a subdisk is 265 sectors smaller than the drive.
.Sh LOG FILE
.Nm
maintains a log file, by default
.Pa /var/tmp/vinum.history ,
in which it keeps track of the commands issued to
.Nm vinum .
You can override the name of this file by setting the environment variable
.Ev VINUM_HISTORY 
to the name of the file.  
.Pp
Each message in the log file is preceded by a date.  The default format is 
.Li %e %b %Y %H:%M:%S
See
.Xr strftime 3
for further details of the format string.  It can be overridden by the
environment variable
.Ev VINUM_DATEFORMAT .
The date format in th
.Sh HOW TO SET UP VINUM
This section gives practical advice about how to implement a
.Nm
system.
.Ss Where to put the data
The first choice you need to make is where to put the data.  You need dedicated
disk partitions for
.Nm vinum .
See the example under DRIVE LAYOUT CONSIDERATIONS above.  Choose partition type
.Nm
unless your version of
.Xr disklabel 8
does not understand this partition type, in which case you will need to use
partition type
.Nm unused
until you update your version of
.Xr disklabel 8 .
Use the compatibility partition (for example,
.Pa /dev/da0g )
rather than the true partition name (such as
.Pa /dev/da0s1g ).
.Nm
currently uses the compatibility partition only for the
.Nm start
command, so this way you can avoid problems.
.Ss Designing volumes
The way you set up
.Nm
volumes depends on your intentions.  There are a number of possibilities:
.Bl -enum
.It
You may want to join up a number of small disks to make a reasonable sized file
system.  For example, if you had five small drives and wanted to use all the
space for a single volume, you might write a configuration file like:
.Bd -literal -offset 4n
drive d1 device /dev/da2e
drive d2 device /dev/da3e
drive d3 device /dev/da4e
drive d4 device /dev/da5e
drive d5 device /dev/da6e
volume bigger
 plex org concat
   sd length 0 drive d1
   sd length 0 drive d2
   sd length 0 drive d3
   sd length 0 drive d4
   sd length 0 drive d5
.Ed
.Pp
In this case, you specify the length of the subdisks as 0, which means 
.if t ``use the largest area of free space that you can find on the drive''.
.if n "use the largest area of free space that you can find on the drive".
If the subdisk is the only subdisk on the drive, it will use all available
space.
.It
You want to set up
.Nm
to obtain additional resilience against disk failures.  You have the choice of
RAID-1, also called 
.if t ``mirroring'', or RAID-5, also called ``parity''.
.if n "mirroring", or RAID-5, also called "parity".
.Pp
To set up mirroring, create multiple plexes in a volume.  For example, to create
a mirrored volume of 2 GB, you might create the following configuration file:
.Bd -literal -offset 4n
drive d1 device /dev/da2e
drive d2 device /dev/da3e
volume mirror
 plex org concat
   sd length 2g drive d1
 plex org concat
   sd length 2g drive d2
.Ed
.Pp
When creating mirrored drives, it is important to ensure that the data from each
plex is on a different physical disk so that
.Nm
can access the complete address space of the volume even if a drive fails.
Note that each plex requires as much data as the complete volume: in this
example, the volume has a size of 2 GB, but each plex (and each subdisk)
requires 2 GB, so the total disk storage requirement is 4 GB.
.Pp
To set up RAID-5, create a single plex of type
.Ar raid5 .  
For example, to create an equivalent resilient volume of 2 GB, you might use the
following configuration file:
.Bd -literal -offset 4n
drive d1 device /dev/da2e
drive d2 device /dev/da3e
drive d3 device /dev/da4e
drive d4 device /dev/da5e
drive d5 device /dev/da6e
volume raid
 plex org raid5 512k
   sd length 512m drive d1
   sd length 512m drive d2
   sd length 512m drive d3
   sd length 512m drive d4
   sd length 512m drive d5
.Ed
.Pp
RAID-5 plexes require at least three subdisks, one of which is used for storing
parity information and is lost for data storage.  The more disks you use, the
greater the proportion of the disk storage can be used for data storage.  In
this example, the total storage usage is 2.5 GB, compared to 4 GB for a mirrored
configuration.  If you were to use the minimum of only three disks, you would
require 3 GB to store the information, for example:
.Bd -literal -offset 4n
drive d1 device /dev/da2e
drive d2 device /dev/da3e
drive d3 device /dev/da4e
volume raid
 plex org raid5 512k
   sd length 1g drive d1
   sd length 1g drive d2
   sd length 1g drive d3
.Ed
.Pp
As with creating mirrored drives, it is important to ensure that the data from
each subdisk is on a different physical disk so that
.Nm
can access the complete address space of the volume even if a drive fails.
.It
You want to set up
.Nm
to allow more concurrent access to a file system.  In many cases, access to a
file system is limited by the speed of the disk.  By spreading the volume across
multiple disks, you can increase the throughput in multi-access environments.
This technique shows little or no performance improvement in single-access
environments.
.Nm
uses a technique called 
.if t ``striping'', 
.if n "striping", 
or sometimes RAID-0, to increase this concurrency of access.  The name RAID-0 is
misleading: striping does not provide any redundancy or additional reliability.
In fact, it decreases the reliability, since the failure of a single disk will
render the volume useless, and the more disks you have, the more likely it is
that one of them will fail.
.Pp
To implement striping, use a
.Ar striped
plex:
.Bd -literal -offset 4n
drive d1 device /dev/da2e
drive d2 device /dev/da3e
drive d3 device /dev/da4e
drive d4 device /dev/da5e
volume raid
 plex org striped 512k
   sd length 512m drive d1
   sd length 512m drive d2
   sd length 512m drive d3
   sd length 512m drive d4
.Ed
.Pp
A striped plex must have at least two subdisks, but the increase in performance
is greater if you have a larger number of disks.
.It
You may want to have the best of both worlds and have both resilience and
performance.  This is sometimes called RAID-10 (a combination of RAID-1 and
RAID-0), though again this name is misleading.  With
.Nm
you can do this with the following configuration file:
.Bd -literal -offset 4n
drive d1 device /dev/da2e
drive d2 device /dev/da3e
drive d3 device /dev/da4e
drive d4 device /dev/da5e
volume raid
 plex org striped 512k
   sd length 512m drive d1
   sd length 512m drive d2
   sd length 512m drive d3
   sd length 512m drive d4
 plex org striped 512k
   sd length 512m drive d4
   sd length 512m drive d3
   sd length 512m drive d2
   sd length 512m drive d1
.Ed
.Pp
Here the plexes are striped, increasing performance, and there are two of them,
increasing reliablity.  Note that this example shows the subdisks of the second
plex in reverse order from the first plex.  This is for performance reasons and
will be discussed below.
.El
.Ss Creating the volumes
Once you have created your configuration files, start
.Nm
and create the volumes.  In this example, the configuration is in the file
.Pa configfile :
.Bd -literal
  # vinum create -v configfile
     1: drive d1 device /dev/da2e
     2: drive d2 device /dev/da3e
     3: volume mirror
     4:  plex org concat
     5:    sd length 2g drive d1
     6:  plex org concat
     7:    sd length 2g drive d2
  Configuration summary
  
  Drives:         2 (4 configured)
  Volumes:        1 (4 configured)
  Plexes:         2 (8 configured)
  Subdisks:       2 (16 configured)
  
  Drive d1:       Device /dev/da2e
                  Created on vinum.lemis.com at Tue Mar 23 12:30:31 1999
                  Config last updated Tue Mar 23 14:30:32 1999
                  Size:      60105216000 bytes (57320 MB)
                  Used:       2147619328 bytes (2048 MB)
                  Available: 57957596672 bytes (55272 MB)
                  State: up
                  Last error: none
  Drive d2:       Device /dev/da3e
                  Created on vinum.lemis.com at Tue Mar 23 12:30:32 1999
                  Config last updated Tue Mar 23 14:30:33 1999 
                  Size:      60105216000 bytes (57320 MB)
                  Used:       2147619328 bytes (2048 MB)
                  Available: 57957596672 bytes (55272 MB)
                  State: up
                  Last error: none
  
  Volume mirror:  Size: 2147483648 bytes (2048 MB)
                  State: up
                  Flags: 
                  2 plexes
                  Read policy: round robin
  
  Plex mirror.p0: Size:   2147483648 bytes (2048 MB)
                  Subdisks:        1
                  State: up
                  Organization: concat
                  Part of volume mirror
  Plex mirror.p1: Size:   2147483648 bytes (2048 MB)
                  Subdisks:        1
                  State: up
                  Organization: concat
                  Part of volume mirror
  
  Subdisk mirror.p0.s0:
                  Size:       2147483648 bytes (2048 MB)
                  State: up
                  Plex mirror.p0 at offset 0
  
  Subdisk mirror.p1.s0:
                  Size:       2147483648 bytes (2048 MB)
                  State: up
                  Plex mirror.p1 at offset 0
.Ed
.Pp
The
.Fl v
flag tells
.Nm
to list the file as it configures.  Subsequently it lists the current
configuration in the same format as the
.Nm list Fl v
command.
.Ss Creating more volumes
Once you have created the
.Nm 
volumes, 
.Nm
keeps track of them in its internal configuration files.  You do not need to
create them again.  In particular, if you run the
.Nm create
command again, you will create additional objects:
.Bd -literal
.if t .ps -2
  # vinum create sampleconfig 
  Configuration summary
  
  Drives:         2 (4 configured)
  Volumes:        1 (4 configured)
  Plexes:         4 (8 configured)
  Subdisks:       4 (16 configured)
  
  D d1                    State: up       Device /dev/da2e        Avail: 53224/57320 MB (92%)
  D d2                    State: up       Device /dev/da3e        Avail: 53224/57320 MB (92%)
  
  V mirror                State: up       Plexes:       4 Size:       2048 MB
  
  P mirror.p0           C State: up       Subdisks:     1 Size:       2048 MB
  P mirror.p1           C State: up       Subdisks:     1 Size:       2048 MB
  P mirror.p2           C State: up       Subdisks:     1 Size:       2048 MB
  P mirror.p3           C State: up       Subdisks:     1 Size:       2048 MB
  
  S mirror.p0.s0          State: up       PO:        0  B Size:       2048 MB
  S mirror.p1.s0          State: up       PO:        0  B Size:       2048 MB
  S mirror.p2.s0          State: up       PO:        0  B Size:       2048 MB
  S mirror.p3.s0          State: up       PO:        0  B Size:       2048 MB
.if t .ps
.Ed
.Pp
As this example (this time with the
.Fl f
flag) shows, re-running the
.Nm create
has created four new plexes, each with a new subdisk.  If you want to add other
volumes, create new configuration files for them.  They do not need to reference
the drives that
.Nm
already knows about.  For example, to create a volume
.Pa raid
on the four drives
.Pa /dev/da1e ,
.Pa /dev/da2e ,
.Pa /dev/da3e 
and
.Pa /dev/da4e ,
you only need to mention the other two:
.Bd -literal
  drive d3 device /dev/da1e
  drive d4 device /dev/da4e
  volume raid
    plex org raid5 512k
      sd size 2g drive d1
      sd size 2g drive d2
      sd size 2g drive d3
      sd size 2g drive d4
.Ed
.Pp
With this configuration file, we get:
.Bd -literal
  # vinum create newconfig
  Configuration summary
  
  Drives:         4 (4 configured)
  Volumes:        2 (4 configured)
  Plexes:         5 (8 configured)
  Subdisks:       8 (16 configured)
  
  D d1                    State: up       Device /dev/da2e        Avail: 51176/57320 MB (89%)
  D d2                    State: up       Device /dev/da3e        Avail: 53220/57320 MB (89%)
  D d3                    State: up       Device /dev/da1e        Avail: 53224/57320 MB (92%)
  D d4                    State: up       Device /dev/da4e        Avail: 53224/57320 MB (92%)
  
  V mirror                State: down     Plexes:       4 Size:       2048 MB
  V raid                  State: down     Plexes:       1 Size:       6144 MB
  
  P mirror.p0           C State: init     Subdisks:     1 Size:       2048 MB
  P mirror.p1           C State: init     Subdisks:     1 Size:       2048 MB
  P mirror.p2           C State: init     Subdisks:     1 Size:       2048 MB
  P mirror.p3           C State: init     Subdisks:     1 Size:       2048 MB
  P raid.p0            R5 State: init     Subdisks:     4 Size:       6144 MB
  
  S mirror.p0.s0          State: up       PO:        0  B Size:       2048 MB
  S mirror.p1.s0          State: up       PO:        0  B Size:       2048 MB
  S mirror.p2.s0          State: up       PO:        0  B Size:       2048 MB
  S mirror.p3.s0          State: up       PO:        0  B Size:       2048 MB
  S raid.p0.s0            State: empty    PO:        0  B Size:       2048 MB
  S raid.p0.s1            State: empty    PO:      512 kB Size:       2048 MB
  S raid.p0.s2            State: empty    PO:     1024 kB Size:       2048 MB
  S raid.p0.s3            State: empty    PO:     1536 kB Size:       2048 MB
.Ed
.Pp
Note the size of the RAID-5 plex: it is only 6 GB, although together its
components use 8 GB of disk space.  This is because the equivalent of one
subdisk is used for storing parity data.
.Ss Restarting Vinum
On rebooting the system, start
.Nm
with the 
.Nm start 
command:
.Bd -literal
  # vinum start
.Ed
.Pp
This will start all the
.Nm
drives in the system.  If for some reason you wish to start only some of them,
use the
.Nm read
command.
.Ss Performance considerations
A number of misconceptions exist about how to set up a RAID array for best
performance.  In particular, most systems use far too small a stripe size.  The
following discussion applies to all RAID systems, not just to
.Nm vinum .
.Pp
The FreeBSD block I/O system issues requests of between .5kB and 60 kB; a
typical mix is somewhere round 8 kB.  You can't stop any striping system from
breaking a request into two physical requests, and if you do it wrong it can be
broken into several.  This will result in a significant drop in performance: the
decrease in transfer time per disk is offset by the order of magnitude greater
increase in latency.
.Pp
With modern disk sizes and the FreeBSD block I/O system, you can expect to have
a reasonably small number of fragmented requests with a stripe size between 256
kB and 512 kB; with correct RAID implementations there is no obvious reason not
to increase the size to 2 or 4 MB on a large disk.
.Pp
The easiest way to consider the impact of any transfer in a multi-access system
is to look at it from the point of view of the potential bottleneck, the disk
subsystem: how much total disk time does the transfer use?  Since just about
everything is cached, the time relationship between the request and its
completion is not so important: the important parameter is the total time that
the request keeps the disks active, the time when the disks are not available to
perform other transfers.  As a result, it doesn't really matter if the transfers
are happening at the same time or different times.  In practical terms, the time
we're looking at is the sum of the total latency (positioning time and
rotational latency, or the time it takes for the data to arrive under the disk
heads) and the total transfer time.  For a given transfer to disks of the same
speed, the transfer time depends only on the total size of the transfer.
.Pp
Consider a typical news article or web page of 24 kB, which will probably be
read in a single I/O.  Take disks with a transfer rate of 6 MB/s and an average
positioning time of 8 ms, and a file system with 4 kB blocks.  Since it's 24 kB,
we don't have to worry about fragments, so the file will start on a 4 kB
boundary.  The number of transfers required depends on where the block starts:
it's (S + F - 1) / S, where S is the stripe size in file system blocks, and F is
the file size in file system blocks.
.Pp
.Bl -enum
.It
Stripe size of 4 kB.  You'll have 6 transfers.  Total subsystem load: 48 ms
latency, 2 ms transfer, 50 ms total.
.It   
Stripe size of 8 kB.  On average, you'll have 3.5 transfers.  Total subsystem
load: 28 ms latency, 2 ms transfer, 30 ms total.
.It   
Stripe size of 16 kB.  On average, you'll have 2.25 transfers.  Total subsystem
load: 18 ms latency, 2 ms transfer, 20 ms total.
.It   
Stripe size of 256 kB.  On average, you'll have 1.08 transfers.  Total subsystem
load: 8.6 ms latency, 2 ms transfer, 10.6 ms total.
.It   
Stripe size of 4 MB.  On average, you'll have 1.0009 transfers.  Total subsystem
load: 8.01 ms latency, 2 ms transfer, 10.01 ms total.
.El   
.Pp
It appears that some hardware RAID systems have problems with large stripes:
they appear to always transfer a complete stripe to or from disk, so that a
large stripe size will have an adverse effect on performance.
.Nm
does not suffer from this problem: it optimizes all disk transfers and does not
transfer unneeded data.
.Pp
Note that no well-known benchmark program tests true multi-access conditions
(more than 100 concurrent users), so it is difficult to demonstrate the validity
of these statements.
.Pp
Given these considerations, the following factors affect the performance of a
.Nm
volume:
.Bl -bullet
.It
Striping improves performance for multiple access only, since it increases the
chance of individual requests being on different drives.
.It
Concatenating UFS file systems across multiple drives can also improve
performance for multiple file access, since UFS divides a file system into
cylinder groups and attempts to keep files in a single cylinder group.  In
general, it is not as effective as striping.
.It
Mirroring can improve multi-access performance for reads, since by default
.Nm
issues consecutive reads to consecutive plexes.
.It
Mirroring decreases performance for all writes, whether multi-access or single
access, since the data must be written to both plexes.  This explains the
subdisk layout in the example of a mirroring configuration above: if the
corresponding subdisk in each plex is on a different physical disk, the write
commands can be issued in parallel, whereas if they are on the same physical
disk, they will be performed sequentially.
.It
RAID-5 reads have essentially the same considerations as striped reads, unless
the striped plex is part of a mirrored volume, in which case the performance of
the mirrored volume will be better.
.It
RAID-5 writes are approximately 25% of the speed of striped writes: to perform
the write,
.Nm
must first read the data block and the corresponding parity block, perform some
calculations and write back the parity block and the data block, four times as
many transfers as for writing a striped plex.  On the other hand, this is offset
by the cost of mirroring, so writes to a volume with a single RAID-5 plex are
approximately half the speed of writes to a correctly configured volume with two
striped plexes.
.It
When the 
.Nm
configuration changes (for example, adding or removing objects, or the change of
state of one of the objects),
.Nm
writes up to 128 kB of updated configuration to each drive.  The larger the
number of drives, the longer this takes.
.El
.Ss Creating file systems on Vinum volumes
You do not need to run
.Nm disklabel
before creating a file system on a
.Nm
volume.  Just run
.Nm newfs
against the raw device.  Use the
.Fl v
option to state that the device is not divided into partitions.  For example, to
create a file system on volume
.Pa mirror ,
enter the following command:
.Bd -literal -offset 4n
# newfs -v /dev/vinum/rmirror
.Ed
.Pp
Note the name
.Pa rmirror ,
indicating the raw device.
.Sh Other considerations
A number of other considerations apply to
.Nm
configuration:
.Bl -bullet
.It
There is no advantage in creating multiple drives on a single disk.  Each drive
uses 131.5 kB of data for label and configuration information, and performance
will suffer when the configuration changes.  Use appropriately sized subdisks instead.
.It
It is possible to increase the size of a concatenated
.Nm
plex, but currently the size of striped and RAID-5 plexes cannot be increased.
Currently the size of an existing UFS file system also cannot be increased, but
it is planned to make both plexes and file systems extensible.
.El
.Sh GOTCHAS
The following points are not bugs, and they have good reasons for existing, but
they have shown to cause confusion.  Each is discussed in the appropriate
section above.
.Bl -enum
.It
.Nm
will not create a device on UFS partitions.  Instead, it will return an error
message 
.if t ``wrong partition type''.  
.if n "wrong partition type".  
The partition type should be
.Ar vinum ,
though currently partitions of type
.Ar unused
are also accepted.
.It
When you create a volume with multiple plexes,
.Nm
does not automatically initialize the plexes.  This means that the contents are
not known, but they are certainly not consistent.  As a result, by default
.Nm
sets the state of all newly-created plexes except the first to
.Ar stale .
In order to synchronize them with the first plex, you must
.Nm start
their subdisks, which causes
.Nm
to copy the data from a plex which is in the
.Ar up
state.  Depending on the size of the subdisks involved, this can take a long
time.
.Pp
In practice, people aren't too interested in what was in the plex when it was
created, and other volume managers cheat by setting them
.Ar up
anyway.
.Nm
provides two ways to ensure that newly created plexes are
.Ar up :
.Bl -bullet
.It
Create the plexes and then synchronize them with
.Nm vinum start .
.It
Create the volume (not the plex) with the keyword
.Ar setupstate ,
which tells
.Nm
to ignore any possible inconsistency and set the plexes to be
.Ar up .
.El
.It
Some of the commands currently supported by
.Nm
are not really needed.  For reasons which I don't understand, however, I find
that users frequently try the
.Nm label
and
.Nm resetconfig
commands, though especially
.Nm resetconfig
outputs all sort of dire warnings.  Don't use these commands unless you have a
good reason to do so.
.It
Some state transitions are not very intuitive.  In fact, it's not clear whether
this is a bug or a feature.  If you find that you can't start an object in some
strange state, such as a
.Ar reborn
subdisk, try first to get it into
.Ar stopped
state, with the
.Nm stop
or
.Nm stop Ar -f
commands.  If that works, you should then be able to start it.  If you find
that this is the only way to get out of a position where easier methods fail,
please report the situation.
.It
If you build the kernel module with the
.Ar -DVINUMDEBUG
option, you must also build
.Nm vinum(8)
with the
.Ar -DVINUMDEBUG
option, since the size of some data objects used by both components depends on
this option.  If you don't do so, commands will fail with the message
.Ar Invalid argument ,
and a console message will be logged such as
.Pp
.Bd -literal
vinumioctl: invalid ioctl from process 247 (vinum): c0e44642
.Ed
.Pp
This error may also occur if you use old versions of kld or userland program.
.It
.Nm
drives are UNIX disk partitions and should have the partition type
.Ar vinum .
This is different from
.Nm ccd ,
which expects partitions of type
.Ar 4.2BSD .
This behaviour of ccd is an invitation to shoot yourself in the foot: with
.Nm ccd 
you can easily overwrite a file system.  
.Nm
will not permit this.
.Pp
For similar reasons, the
.Nm vinum Ar start
command will not accept a drive on partition
.Ar c .
Partition
.Ar c
is used by the system to represent the whole disk, and must be of type
.Ar unused .
Clearly there is a conflict here, which
.Nm
resolves by not using the
.Ar c
partition.
.It
The
.Nm vinum Ar read
command has a particularly emetic syntax.  Once it was the only way to start
.Nm vinum ,
but now the preferred method is with
.Nm vinum Ar start .
.Nm vinum Ar read
should be used for maintenance purposes only.  Note that its syntax has changed,
and the arguments must be disk slices, such as
.Pa /dev/da0 ,
not partitions such as
.Pa /dev/da0e .
.El
.\"XXX.Sh BUGS
.Sh FILES
.Ar /dev/vinum
- directory with device nodes for
.Nm
objects.
.br
.Ar /dev/vinum/control
- control device for
.Nm vinum
.br
.Ar /dev/vinum/plex
- directory containing device nodes for
.Nm
plexes.
.br
.Ar /dev/vinum/sd
- directory containing device nodes for
.Nm
subdisks.
.Sh ENVIRONMENT VARIABLES
.Bl -hang
.It VINUM_HISTORY
The name of the log file, by default /var/log/vinum_history.
.It VINUM_DATEFORMAT
The format of dates in the log file, by default %e %b %Y %H:%M:%S.
.It EDITOR
The name of the editor to use for editing configuration files, by default
.Nm vi .
.El
.Sh SEE ALSO
.Xr vinum 4 ,
.Xr disklabel 8 ,
.Xr newfs 8 ,
.Xr strftime 3 ,
.Pa http://www.lemis.com/vinum.html ,
.Pa http://www.lemis.com/vinum-debugging.html .
.Sh AUTHOR
Greg Lehey
.Pa <grog@lemis.com> .
.Sh HISTORY
The
.Nm
command first appeared in FreeBSD 3.0.