freebsd-dev/sbin/tunefs/tunefs.8
Kirk McKusick baa12a84a7 The purpose of this change to the FFS layout policy is to reduce the
running time for a full fsck. It also reduces the random access time
for large files and speeds the traversal time for directory tree walks.

The key idea is to reserve a small area in each cylinder group
immediately following the inode blocks for the use of metadata,
specifically indirect blocks and directory contents. The new policy
is to preferentially place metadata in the metadata area and
everything else in the blocks that follow the metadata area.

The size of this area can be set when creating a filesystem using
newfs(8) or changed in an existing filesystem using tunefs(8).
Both utilities use the `-k held-for-metadata-blocks' option to
specify the amount of space to be held for metadata blocks in each
cylinder group. By default, newfs(8) sets this area to half of
minfree (typically 4% of the data area).

This work was inspired by a paper presented at Usenix's FAST '13:
www.usenix.org/conference/fast13/ffsck-fast-file-system-checker

Details of this implementation appears in the April 2013 of ;login:
www.usenix.org/publications/login/april-2013-volume-38-number-2.
A copy of the April 2013 ;login: paper can also be downloaded
from: www.mckusick.com/publications/faster_fsck.pdf.

Reviewed by: kib
Tested by:   Peter Holm
MFC after:   4 weeks
2013-03-22 21:45:28 +00:00

209 lines
7.2 KiB
Groff

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.\" @(#)tunefs.8 8.2 (Berkeley) 12/11/93
.\" $FreeBSD$
.\"
.Dd June 22, 2011
.Dt TUNEFS 8
.Os
.Sh NAME
.Nm tunefs
.Nd tune up an existing UFS file system
.Sh SYNOPSIS
.Nm
.Op Fl A
.Op Fl a Cm enable | disable
.Op Fl e Ar maxbpg
.Op Fl f Ar avgfilesize
.Op Fl j Cm enable | disable
.Op Fl J Cm enable | disable
.Op Fl k Ar held-for-metadata-blocks
.Op Fl L Ar volname
.Op Fl l Cm enable | disable
.Op Fl m Ar minfree
.Op Fl N Cm enable | disable
.Op Fl n Cm enable | disable
.Op Fl o Cm space | time
.Op Fl p
.Op Fl s Ar avgfpdir
.Op Fl S Ar size
.Op Fl t Cm enable | disable
.Ar special | filesystem
.Sh DESCRIPTION
The
.Nm
utility is designed to change the dynamic parameters of a UFS file system
which affect the layout policies.
The
.Nm
utility cannot be run on an active file system.
To change an active file system,
it must be downgraded to read-only or unmounted.
.Pp
The parameters which are to be changed are indicated by the flags
given below:
.Bl -tag -width indent
.It Fl A
The file system has several backups of the super-block.
Specifying
this option will cause all backups to be modified as well as the
primary super-block.
This is potentially dangerous - use with caution.
.It Fl a Cm enable | disable
Turn on/off the administrative POSIX.1e ACL enable flag.
.It Fl e Ar maxbpg
Indicate the maximum number of blocks any single file can
allocate out of a cylinder group before it is forced to begin
allocating blocks from another cylinder group.
Typically this value is set to about one quarter of the total blocks
in a cylinder group.
The intent is to prevent any single file from using up all the
blocks in a single cylinder group,
thus degrading access times for all files subsequently allocated
in that cylinder group.
The effect of this limit is to cause big files to do long seeks
more frequently than if they were allowed to allocate all the blocks
in a cylinder group before seeking elsewhere.
For file systems with exclusively large files,
this parameter should be set higher.
.It Fl f Ar avgfilesize
Specify the expected average file size.
.It Fl j Cm enable | disable
Turn on/off soft updates journaling.
.It Fl J Cm enable | disable
Turn on/off gjournal flag.
.It Fl k Ar held-for-metadata-blocks
Set the amount of space to be held for metadata blocks.
When set, the file system preference routines will try to save
the specified amount of space immediately following the inode blocks
in each cylinder group for use by metadata blocks.
Clustering the metadata blocks speeds up random file access
and decreases the running time of
.Xr fsck 8 .
While this option can be set at any time,
it is most effective if set before any data is loaded into the file system.
By default
.Xr newfs 8
sets it to half of the space reserved to minfree.
.It Fl L Ar volname
Add/modify an optional file system volume label.
.It Fl l Cm enable | disable
Turn on/off MAC multilabel flag.
.It Fl m Ar minfree
Specify the percentage of space held back
from normal users; the minimum free space threshold.
The default value used is 8%.
Note that lowering the threshold can adversely affect performance:
.Bl -bullet
.It
Settings of 5% and less force space optimization to
always be used which will greatly increase the overhead for file
writes.
.It
The file system's ability to avoid fragmentation will be reduced
when the total free space, including the reserve, drops below 15%.
As free space approaches zero, throughput can degrade by up to a
factor of three over the performance obtained at a 10% threshold.
.El
.Pp
If the value is raised above the current usage level,
users will be unable to allocate files until enough files have
been deleted to get under the higher threshold.
.It Fl N Cm enable | disable
Turn on/off the administrative NFSv4 ACL enable flag.
.It Fl n Cm enable | disable
Turn on/off soft updates.
.It Fl o Cm space | time
The file system can either try to minimize the time spent
allocating blocks, or it can attempt to minimize the space
fragmentation on the disk.
Optimization for space has much
higher overhead for file writes.
The kernel normally changes the preference automatically as
the percent fragmentation changes on the file system.
.It Fl p
Show a summary of what the current tunable settings
are on the selected file system.
More detailed information can be
obtained from the
.Xr dumpfs 8
utility.
.It Fl s Ar avgfpdir
Specify the expected number of files per directory.
.It Fl S Ar size
Specify the softdep journal size in bytes.
The minimum is 4M.
.It Fl t Cm enable | disable
Turn on/off the TRIM enable flag.
If enabled, and if the underlying device supports the BIO_DELETE
command, the file system will send a delete request to the underlying
device for each freed block.
The trim enable flag is typically set when the underlying device
uses flash-memory as the device can use the delete command to
pre-zero or at least avoid copying blocks that have been deleted.
.El
.Pp
At least one of the above flags is required.
.Sh FILES
.Bl -tag -width ".Pa /etc/fstab"
.It Pa /etc/fstab
read this to determine the device file for a
specified mount point.
.El
.Sh SEE ALSO
.Xr fs 5 ,
.Xr dumpfs 8 ,
.Xr gjournal 8 ,
.Xr growfs 8 ,
.Xr newfs 8
.Rs
.%A M. McKusick
.%A W. Joy
.%A S. Leffler
.%A R. Fabry
.%T "A Fast File System for UNIX"
.%J "ACM Transactions on Computer Systems 2"
.%N 3
.%P pp 181-197
.%D August 1984
.%O "(reprinted in the BSD System Manager's Manual, SMM:5)"
.Re
.Sh HISTORY
The
.Nm
utility appeared in
.Bx 4.2 .
.Sh BUGS
This utility does not work on active file systems.
To change the root file system, the system must be rebooted
after the file system is tuned.
.\" Take this out and a Unix Daemon will dog your steps from now until
.\" the time_t's wrap around.
.Pp
You can tune a file system, but you cannot tune a fish.