.\" SCCSID: @(#)tunefs.8 8.1 9/11/90 .TH tunefs 8 .SH Name tunefs \- tune up an existing file system .SH Syntax .B /etc/tunefs [ .I options ] .SH Description .NXR "tunefs command" .NXR "file system" "changing layout policy" The .PN tunefs command 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 options listed in the following section. .SH Options .NXR "tunefs command" "options" .IP "\fB\-a\fP maxcontig" 10 This specifies the maximum number of contiguous blocks that will be laid out before forcing a rotational delay (see \fB\-d\fR 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. .IP "\fB\-d\fP 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. .IP "\fB\-e\fP 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 elsewhere. For file systems with exclusively large files, this parameter should be set higher. .IP "\fB\-m\fP 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 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. .IP \-c Clean byte timeout factor. The metrics used to determine if a clean byte associated with a file system should be invalidated, decrement a timeout factor when crossed. When the timeout factor reaches zero, the clean byte is invalidated and .PN fsck 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 .PN fsck to check the file system on every reboot. .SH Restrictions .NXR "tunefs command" "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. .SH See Also fs(5), fsck(8), mkfs(8), newfs(8) .br ``A Fast File System for UNIX,'' .I "ULTRIX Supplementary Documents, Volume 3: System Manager"
