TUNEFS(8) NetBSD System Manager's Manual TUNEFS(8)
NAME
tunefs - tune up an existing file system
SYNOPSIS
tunefs [-AFN] [-a maxcontig] [-d rotdelay] [-e maxbpg] [-g avgfilesize] [-h avgfpdir] [-k trackskew] [-m minfree] [-o optimize_preference] special | filesys
DESCRIPTION
tunefs is designed to change the dynamic parameters of a file system which affect the layout policies. The following options are supported by tunefs: -A Cause the values to be updated in all the alternate superblocks instead of just the standard superblock. If this option is not used, then use of a backup superblock by fsck(8) will lose any- thing changed by tunefs. -A is ignored when -N is specified. -F Indicates that special is a file system image, rather than a de- vice name or file system mount point. special will be accessed `as-is'. -N Display all the settable options (after any changes from the tun- ing options) but do not cause any of them to be changed. -a maxcontig This specifies the maximum number of contiguous blocks that will be laid out before forcing a rotational delay (see -d below). The default value is one, since most device drivers require an interrupt per disk transfer. Device drivers that can chain sev- eral buffers together in a single transfer should set this to the maximum chain length. -d rotdelay This 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. -e maxbpg This indicates the maximum number of blocks any single file can allocate out of a cylinder group before it is forced to begin al- locating blocks from another cylinder group. Typically this val- ue 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. -g avgfilesize This specifies the expected average file size. -h avgfpdir This specifies the expected number of files per directory. -k trackskew This specifies the skew in sectors from one track to the next in a cylinder. The default value is zero, indicating that each track in a cylinder begins at the same rotational position. -m minfree This value specifies the percentage of space held back from nor- mal users; the minimum free space threshold. The default value used is 10%. This value can be set to zero, however up to a fac- tor of three in throughput will be lost over the performance ob- tained 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 high- er threshold. -o optimize_preference The file system can either try to minimize the time spent allo- cating blocks, or it can attempt to minimize the space fragmenta- tion on the disk. 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 problemati- cal, and the file system can be optimized for time. optimize_preference can be specified as either space or time.
SEE ALSO
fs(5), dumpfs(8), fsck_ffs(8), newfs(8) M. McKusick, W. Joy, S. Leffler, and R. Fabry, "A Fast File System for UNIX", ACM Transactions on Computer Systems 2, 3, pp 181-197, August 1984, (reprinted in the BSD System Manager's Manual, SMM:5).
HISTORY
The tunefs command appeared in 4.2BSD.
BUGS
This program should work on mounted and active file systems. Because the super-block is not kept in the buffer cache, the changes will only take effect if the program is run on unmounted file systems. To change the root file system, the system must be rebooted after the file system is tuned. You can tune a file system, but you can't tune a fish. NetBSD 1.6.2 November 9, 2001 2
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