tunefs man page on Tru64

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tunefs(8)							     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

OPTIONS
       Specifies the maximum number of contiguous blocks that will be laid out
       before  forcing	a  rotational  delay (see the -d option).  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  allocat‐
       ing  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 subse‐
       quently	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  parame‐
       ter  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 the previous	 list  item)  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 a
	      problem, and the file system can be optimized for time.

OPERANDS
       Specifies the UFS file system that is being tuned.

DESCRIPTION
       The tunefs command changes the dynamic parameters of a UFS file	system
       that affect the layout policies. The parameters to be changed are indi‐
       cated by the options specified.

       You should unmount a file system before running the tunefs program. The
       tunefs  program	does  allow  you to enter parameters for a mounted and
       active file system.  However, your changes will not take	 effect	 until
       the file system is unmounted and mounted again (or until after the sys‐
       tem is rebooted). If you use  tunefs  to	 tune  the  root  file	system
       (assuming root is a UFS file system), you must always reboot the system
       in order for your changes to take effect.

       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.

       After you specify an optimization preference, it comes into  play  only
       under the following conditions: A file is growing It is not possible to
       extend a fragment There is a choice between allocating  an  exact-sized
       fragment	 or  allocating a full block and freeing the unused portion of
       the block

       After you specify an optimization preference, the  system  first	 tries
       the  specified  preference  when	 it reaches the minimum reserved space
       specified by the minfree value. If you specified -o space,  the	system
       tries space optimization, but switches to time optimization if the file
       continues to grow and fragmentation is less than half  of  the  minimum
       free  reserve. If you specifed -o time, the system tries time optimiza‐
       tion, but switches to space optimization if 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.

SEE ALSO
       Commands: newfs(8)

								     tunefs(8)
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