tunefs(8)tunefs(8)Nametunefs - tune up an existing file system
Syntax
/etc/tunefs [ options ]
Description
The command is designed to change the dynamic parameters of a file sys‐
tem which affect the layout policies. The parameters which are to be
changed are indicated by the options listed in the following section.
Options-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 several 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. Typi‐
cally 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 exclu‐
sively large files, this parameter should be set higher.
-m minfree
This value 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 per‐
formance 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.
-c Clean byte timeout factor. The metrics used to determine if a
clean byte associated with a file system should be invali‐
dated, decrement a timeout factor when crossed. When the
timeout factor reaches zero, the clean byte is invalidated
and will automatically check the file system. The timeout
factor can be increased to a value between 0 and 255. A value
of zero will cause to check the file system on every reboot.
Restrictions
This program should work on mounted and active file systems. Because
the super-block is not kept in the buffer cache, the program will only
take effect if it is run on dismounted file systems. If run on the
root file system, the system must be rebooted.
See Alsofs(5), fsck(8), mkfs(8), newfs(8)
``A Fast File System for UNIX,'' ULTRIX Supplementary Documents, Volume
3: System Manager
tunefs(8)
