tunefs(8) System Manager's Manual tunefs(8)
NAME
tunefs - Tunes an existing UFS file system
SYNOPSIS
/usr/sbin/tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree] [-o optimization_preference] file_system
FLAGS
Specifies the maximum number of contiguous blocks that will be laid out before forcing a rotational delay (see the -d flag). The default
value is 8. Device drivers that can chain several buffers together in a single transfer should set this to the maximum chain length.
Specifies the expected time (in milliseconds) to service a transfer completion interrupt and initiate a new transfer on the same disk. It
is used to decide how much rotational spacing to place between successive blocks in a file. Indicates 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,
you set this value 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. Specifies
the percentage of space held back from normal users; the minimum free space threshold. The default value used is 10%. This value can be
set to zero, however up to a factor of three in throughput will be lost over the performance obtained at a 10% threshold. Note that 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. Specifies whether the file system should try to minimize the time spent allocating blocks (-o time) or try to minimize
the space fragmentation on the disk (-o space). If the value of minfree (see above) is less than 10%, then the file system should optimize
for space to avoid running out of full sized blocks. For values of minfree greater than or equal to 10%, fragmentation is unlikely to be
problematical, and the file system can be optimized for time.
DESCRIPTION
The tunefs command changes the dynamic parameters of a UFS file system which affect the layout policies. The parameters which are to be
changed are indicated by the flags specified.
This program should work on mounted and active file systems. Because the superblock is not kept in the buffer cache, the changes will only
take effect if the program is run on unmounted file systems.
The system must be rebooted after the root file system is tuned.
For larger-capacity devices, set minfree to five percent.
The rotdelay value is useful for disks that do not have read-ahead cache, such as the RA-series disks. For disks that have read-ahead
cache, set rotdelay to zero.
When you specifiy an optimization preference, it only comes into play in the following circumstances: when a file is growing; when it is
not possible to extend a fragment; and when there is a choice between the following paths: Allocating an exact-sized fragment Allocating a
full block and freeing the unused portion of the block When you specify an optimization preference, the system will first try that method
when it reaches the minimum reserved space specified in minfree. If you specify space optimization, the system will try that, but switch
to time optimization when the file continues to grow and fragmentation is less than half of the minimum free reserve. If you specify time
optimization, the system will try that, but switch to space optimization when the file growth causes disk fragmentation to reach within two
percent of the minimum free reserve.
You must be the root user to use this command.
FILES
Specifies the command path
RELATED INFORMATION
Commands: newfs(8) delim off
tunefs(8)