Sun Microsystems Sun Workstation 100U System Manager's Manual page 263

TUNEFS(8)
MAINTENANCE COMMANDS
TUNEFS(8)
NAME
tunefs - tune up an existing file system
SYNOPSIS
Jete/tuner.
tuneup-optionB specitJllfileBYB
DESCRIPTION
Tune/s is designed to change the dynamic parameters of a file system which aJlect the layout poli-
cies. The parameters which are to be changed are indicated by the flags given below:
-. maxcontig
This specifies the maximum number of contiguous blocks that will be laid out before forc-
ing 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 inter-
rupt and initiate a new transfer on the same disk. It is used to decide how much rota-
tional 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 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 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 normal users; the minimum
free space threshold. The default value used is 10% .. This value can be set to zero, how-
ever 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.
SEE ALSO
BUGS
108
fs(5), newfs(8), mkfs(S)
McKusick, Joy, Lemer; "A Fast File System for Unix", Computer Systems Research Group, Dept
of EECS, Berkeley, CA 94720; TR #7, September 1982.
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)
Last change: 20 February 1983
Sun Release 1.1