TUNEFS(8)TUNEFS(8)NAMEtunefs - tune up an existing file system
SYNOPSIStunefs tuneup-options special|filesys
DESCRIPTION
Tunefs is designed to change the dynamic parameters of a file system
which affect the layout policies. The parameters which are to be
changed are indicated by the flags given below:
-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
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 degrad‐
ing 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 else‐
where. For file systems with exclusively large files, this
parameter should be set higher.
-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
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.
-o optimization preference
The file system can either try to minimize the time spent allo‐
cating blocks, or it can attempt 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
problematical, and the file system can be optimized for time.
SEE ALSOfs(5), newfs(8), mkfs(8)
M. McKusick, W. Joy, S. Leffler, R. Fabry, ``A Fast File System for
UNIX'', ACM Transactions on Computer Systems 2, 3. pp 181-197, August
1984. (reprinted in the System Manager's Manual, SMM:14)
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 dismounted 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.
4.2 Berkeley Distribution June 24, 1990 TUNEFS(8)
