Add a man page.
This commit is contained in:
mjacob
parent
325fee4370
commit
ffe78e7e5c
@ -2,8 +2,6 @@
|
||||
|
||||
.PATH: ${.CURDIR}/../../misc
|
||||
CLASS= multipath
|
||||
NO_MAN=true
|
||||
|
||||
|
||||
.include <bsd.lib.mk>
|
||||
|
||||
|
||||
250
sbin/geom/class/multipath/gmultipath.8
Normal file
250
sbin/geom/class/multipath/gmultipath.8
Normal file
@ -0,0 +1,250 @@
|
||||
.\" Copyright (c) 2007 Matthew Jacob
|
||||
.\" All rights reserved.
|
||||
.\"
|
||||
.\" Redistribution and use in source and binary forms, with or without
|
||||
.\" modification, are permitted provided that the following conditions
|
||||
.\" are met:
|
||||
.\" 1. Redistributions of source code must retain the above copyright
|
||||
.\" notice, this list of conditions and the following disclaimer.
|
||||
.\" 2. Redistributions in binary form must reproduce the above copyright
|
||||
.\" notice, this list of conditions and the following disclaimer in the
|
||||
.\" documentation and/or other materials provided with the distribution.
|
||||
.\"
|
||||
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
|
||||
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
||||
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
||||
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
|
||||
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
||||
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
||||
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
||||
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
||||
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
||||
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
||||
.\" SUCH DAMAGE.
|
||||
.\"
|
||||
.\" $FreeBSD$
|
||||
.\"
|
||||
.Dd February 26, 2007
|
||||
.Dt GMULTIPATH 8
|
||||
.Os
|
||||
.Sh NAME
|
||||
.Nm gmultipath
|
||||
.Nd "disk multipath control utility"
|
||||
.Sh SYNOPSIS
|
||||
.Nm
|
||||
.Cm label
|
||||
.Op Fl hv
|
||||
.Ar name
|
||||
.Ar prov ...
|
||||
.Nm
|
||||
.Cm clear
|
||||
.Op Fl v
|
||||
.Ar prov ...
|
||||
.Nm
|
||||
.Cm list
|
||||
.Nm
|
||||
.Cm status
|
||||
.Nm
|
||||
.Cm load
|
||||
.Nm
|
||||
.Cm unload
|
||||
.Sh DESCRIPTION
|
||||
The
|
||||
.Nm
|
||||
utility is used for device multipath configuration.
|
||||
.Pp
|
||||
Only automatic configuration is supported at the present time via the
|
||||
.It Cm label
|
||||
command. This operation writes a label on the last sector of the underlying
|
||||
disk device with a contained name and UUID. The UUID guarantees uniqueness
|
||||
in in a shared storage environment but is in general too cumbersome to use.
|
||||
The name is what is exported via the devcice interface.
|
||||
.Pp
|
||||
The first argument to
|
||||
.Nm
|
||||
indicates an action to be performed:
|
||||
.Bl -tag -width ".Cm destroy"
|
||||
.It Cm label
|
||||
Label the given underlying device with the specified
|
||||
.Ar name .
|
||||
The kernel module
|
||||
.Pa geom_multipath.ko
|
||||
will be loaded if it is not loaded already.
|
||||
.It Cm clear
|
||||
Clear metadata on the given device.
|
||||
.It Cm list
|
||||
See
|
||||
.Xr geom 8 .
|
||||
.It Cm status
|
||||
See
|
||||
.Xr geom 8 .
|
||||
.It Cm load
|
||||
See
|
||||
.Xr geom 8 .
|
||||
.It Cm unload
|
||||
See
|
||||
.Xr geom 8 .
|
||||
.El
|
||||
.Pp
|
||||
.El
|
||||
.Sh SYSCTL VARIABLES
|
||||
The following
|
||||
.Xr sysctl 8
|
||||
variable can be used to control the behavior of the
|
||||
.Nm MULTIPATH
|
||||
GEOM class.
|
||||
.Bl -tag -width indent
|
||||
.It Va kern.geom.multipath.debug : No 0
|
||||
Debug level of the
|
||||
.Nm MULTIPATH
|
||||
GEOM class.
|
||||
This can be set to 0 (default) or 1 to disable or enable various
|
||||
forms of chattiness.
|
||||
.El
|
||||
.Sh EXIT STATUS
|
||||
Exit status is 0 on success, and 1 if the command fails.
|
||||
.Sh MULTIPATH ARCHITECTURE
|
||||
.Pp
|
||||
This is an active/passive
|
||||
multiple path architecture with no device knowledge or presumptions other
|
||||
than size matching built in. Therefore the user must exercise some care
|
||||
in selecting providers that do indeed represent multiple paths to the
|
||||
same underlying disk device. The reason for this is that there are several
|
||||
criteria across multiple underlying transport types that can
|
||||
.Ar indicate
|
||||
identity, but in all respects such identity can rarely be considered
|
||||
.Ar definitive .
|
||||
.Pp
|
||||
For example, if you use the World Word Port Name of a Fibre Channel
|
||||
disk object you might believe that two disks that have the same WWPN
|
||||
on different paths (or even disjoint fabrics) might be considered
|
||||
the same disk. Nearly always this would be a safe assumption, until
|
||||
you realize that a WWPN, like an Ethernet MAC address, is a soft
|
||||
programmable entity, and that a misconfigured Director Class switch
|
||||
could lead you to believe that incorrectly that you've found multiple
|
||||
paths to the same device. This is an extreme and theoretical case, but
|
||||
it is possible enough to indicate that the policy for deciding which
|
||||
of multiple pathnames refer to the same device should be left to the
|
||||
system operator who will use tools and knowledge of their own storage
|
||||
subsystem to make the correct configuration selection.
|
||||
.Pp
|
||||
As an active/passive architecture, only one path has I/O moving on it
|
||||
at any point in time. This I/O continues until an I/O is returned with
|
||||
a generic I/O error or a "Nonexistent Device" error. When this occurs,
|
||||
the active device is kicked out of the
|
||||
.Nm MULTIPATH
|
||||
GEOM class and the next in a list is selected, the failed I/O reissued
|
||||
and the system proceeds.
|
||||
.Pp
|
||||
When new devices are added to the system the
|
||||
.Nm MULTIPATH
|
||||
GEOM class is given an opportunity to taste these new devices. If a new
|
||||
device has a
|
||||
.Nm MULTIPATH
|
||||
label, the device is used to either create a new
|
||||
.Nm MULTIPATH
|
||||
GEOM, or to attach to the end of the list of devices for an existing
|
||||
.Nm MULTIPATH
|
||||
GEOM.
|
||||
.Pp
|
||||
It is this mechanism that works reasonably with
|
||||
.Xr isp 4
|
||||
and
|
||||
.Xr mpt 4
|
||||
based Fibre Channel disk devices. For these devices, when a device disappears
|
||||
(due, e.g., to a cable pull or power failure to a switch), the device is
|
||||
proactively marked as gone and I/O to it failed. This causes the
|
||||
.Nm MULTIPATH
|
||||
failure event just described.
|
||||
.Pp
|
||||
When Fibre Channel events inform either
|
||||
.Xr isp 4
|
||||
or
|
||||
.Xr mpt 4
|
||||
host bus adapters that new devices may have arrived (e.g., the arrival
|
||||
of an RSCN event from the Fabric Domain Controller), they can cause
|
||||
a rescan to occur and cause the attachment and configuration of any
|
||||
(now) new devices to occur, causing the taste event describe above.
|
||||
.Pp
|
||||
This means that this active/passive architecture is not a one-shot path
|
||||
failover, but can be considered to be steady state as long as failed
|
||||
paths are repaired (automatically or otherwise).
|
||||
.Pp
|
||||
Automatic rescanning is not a requirement. Nor is Fibre Channel. The
|
||||
same failover mechanisms work equally well for traditional "Parallel"
|
||||
SCSI but require manual intervention with
|
||||
.Xr camcontrol 8
|
||||
to cause the reattachment of repaired device links.
|
||||
.Sh EXAMPLES
|
||||
The following example shows how to use
|
||||
.Xr camcontrol 8
|
||||
to find possible multiple path devices and to create a
|
||||
.Nm MULTIPATH
|
||||
GEOM class for them.
|
||||
.Bd -literal -offset indent
|
||||
mysys# camcontrol devlist
|
||||
<ECNCTX @WESTVILLE > at scbus0 target 0 lun 0 (da0,pass0)
|
||||
<ECNCTX @WESTVILLE > at scbus0 target 0 lun 1 (da1,pass1)
|
||||
<ECNCTX @WESTVILLE > at scbus1 target 0 lun 0 (da2,pass2)
|
||||
<ECNCTX @WESTVILLE > at scbus1 target 0 lun 1 (da3,pass3)
|
||||
mysys# camcontrol inquiry da0 -S
|
||||
ECNTX0LUN000000SER10ac0d01
|
||||
mysys# camcontrol inquiry da2 -S
|
||||
ECNTX0LUN000000SER10ac0d01
|
||||
.Ed
|
||||
.Pp
|
||||
Now that you've used the Serial Number to compare two disk paths
|
||||
it's not entirely unreasonable to conclude that these are multiple
|
||||
paths to the same device. However, only the user who is familiar
|
||||
with their storage is qualified to make this judgement.
|
||||
.Pp
|
||||
You can then use the
|
||||
.Nm
|
||||
command to label and create the
|
||||
.Nm MULTIPATH
|
||||
GEOM class named
|
||||
.Ar data .
|
||||
.Bd -literal -offset indent
|
||||
gmultipath label -v Fred /dev/da0 /dev/da2
|
||||
disklabel -Brw /dev/multipath/Fred auto
|
||||
newfs /dev/multipath/Freda
|
||||
mount /dev/mutlpath/Freda /mnt....
|
||||
.Ed
|
||||
.Pp
|
||||
The resultant console output looks something like:
|
||||
.Bd -literal -offset indent
|
||||
GEOM_MULTIPATH: adding da0 to Fred/b631385f-c61c-11db-b884-0011116ae789
|
||||
GEOM_MULTIPATH: da0 now active path in Fred
|
||||
GEOM_MULTIPATH: adding da2 to Fred/b631385f-c61c-11db-b884-0011116ae789
|
||||
.Ed
|
||||
.Sh
|
||||
.Sh SEE ALSO
|
||||
.Xr geom 4 ,
|
||||
.Xr isp 4,
|
||||
.Xr mpt 4,
|
||||
.Xr loader.conf 5 ,
|
||||
.Xr camcontrol 8 ,
|
||||
.Xr geom 8 ,
|
||||
.Xr mount 8 ,
|
||||
.Xr newfs 8 ,
|
||||
.Xr sysctl 8 ,
|
||||
.Sh BUGS
|
||||
The
|
||||
.Nm
|
||||
should allow for a manual method of pairing disks.
|
||||
.Pp
|
||||
There is currently no way for
|
||||
.Pa geom_multipath.ko
|
||||
to distinguish between various label instances of the same provider. That
|
||||
is devices such as
|
||||
.Ar da0
|
||||
and
|
||||
.Ar da0c
|
||||
can be tasted and instantiated as multiple paths for the same device.
|
||||
Technically, this is correct, but pretty useless. This will be fixed soon
|
||||
(I hope), but to avoid this it's a good idea to destroy any label on
|
||||
the disk object prior to labelling it with
|
||||
.Nm .
|
||||
.Fx 7.0 .
|
||||
.Sh AUTHOR
|
||||
.An Matthew Jacob Aq mjacob@FreeBSD.org
|
||||
Loading…
Reference in New Issue
Block a user