tunefs(1M) tunefs(1M)NAME tunefs - tunes a Berkeley 4.2 (UFS) file system SYNOPSIS tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m free-space] [-o optimization] [-p] disk-device-file ARGUMENTS -a maxcontig Specifies the maximum number of contiguous blocks to allocate before forcing a rotational delay. The value of maxcontig must be greater than 0 and less than or equal to 200. When newfs makes a UFS file system, it uses a default value of 1 because most device drivers require an interrupt per disk transfer. -d rotdelay Specifies in milliseconds the rotational delay. The value of rotdelay must be greater than or equal to 0 and less than or equal to 16 and is used to decide how much rotational spacing to place between successive blocks in a file. When newfs makes a UFS file system, it uses a default value of 4. disk-device-file Specifies the name of the device file whose tunable parameters are to be displayed or changed. The format of a device file name is cndnsn, where n is a single number. The number that follows the c corresponds to a SCSI device number. An example value for disk-device-file is /dev/rdsk/c0d0s0. Another example is /dev/rfloppy0. -e maxbpg Specifies the maximum number of blocks that can be allocated out of a cylinder group for any single file before the allocation of blocks from another cylinder group is forced. When newfs makes a file system, it calculates a value for maxbpg that is derived from the block size and the size of the cg structure. For file systems with exclusively large files, the value of maxbpg should be set higher. Typically, maxbpg is set to 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, which would degrade access times for files that are subsequently allocated in that cylinder group. The effect of this limit is that big files cause long seeks more frequently than if they were allocated all the blocks in a cylinder group before seeking elsewhere. January 1992 1
tunefs(1M) tunefs(1M)-m free-space Specifies as a percentage of the total available space in the file system the amount of space that cannot be used by users who are not logged in as root. You can specify a value of 0, although up to a factor of three inthroughput is lost over the performance obtained when free-space has a value of 10. When newfs makes a file system, it uses a default value of 10. Note that if the value of free-space is raised above the current usage level, users cannot allocate files until enough files are deleted to satisfy the limit imposed by the higher threshold. -o optimization Specifies an optimization strategy. The value of optimization can be time or space. A value of time minimizes the time spent allocating blocks, and a value of space minimizes space fragmentation on the disk. If the value of the free-space argument is less than 10 percent you should use a value of space to avoid running out of full-sized blocks. When the value of free-space is greater than or equal to 10 percent- fragmentation is unlikely to be a problem, and you should use a value of time to optimize the allocation of blocks. When newfs makes a file system, it uses the same algorithm to determine the value of optimization. -p Prints the current values of the maximum number of contiguous blocks, rotation delay, blocks per cylinder group, minimum free space, and optimization parameters. DESCRIPTION tunefs displays the value of the tunable parameters of a Berkeley 4.2 file system (UFS). You can also use tunefs to change the tunable parameters. UFS file systems are created by the newfs command, which stores the tunable parameters in the superblock of the file system. Because the superblock is not kept in the kernel's buffer cache, you must unmount the file system before running tunefs. When you next mount the file system, the new parameters take effect. To change the tunable parameters of the root file system, you must reboot the system after running tunefs. STATUS MESSAGES AND VALUES The tunefs command prints this message when you change the value of maxcontig to 10: maximum contiguous block count changes from 1 to 10 2 January 1992
tunefs(1M) tunefs(1M)The tunefs command prints this message when you change the value of rotdelay to 6: rotational delay between contiguous blocks changes from 4ms to 6ms The tunefs command prints this message when you change the value of maxbpg to 128: maximum blocks per file in a cylinder group changes from 256 to 128 The tunefs command prints this message when you change the value of minfree to 8 when optimization is set to time: minimum percentage of free space changes from 10% to 8% should optimize for space with minfree < 10% The tunefs command prints this message when you change the value of optimization to space when the value of minfree is greater than or equal to 10: optimization preference changes from time to space should optimize for time with minfree >= 10% NOTES On systems with device drivers that can chain several buffers together in a single transfer, you should set maxcontig to the maximum chain length. FILES /etc/fs/ufs/tunefs Executable file /etc/tunefs File containing a symbolic link to /etc/fs/ufs/tunefs SEE ALSO newfs(1M) ufs(4) in A/UX Programmer's Reference January 1992 3