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Modify files
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tunefs(1M) tunefs(1M) NAME
tunefs - tune up an existing HFS file system SYNOPSIS
maxcontig] rotdelay] maxbpg] minfree] advanced read-ahead] special-device DESCRIPTION
The command is used to alter dynamic parameters that affect HFS file system layout policies. Parameters to be altered are specified by the options and arguments provided on the command line as described below. affects how the file system blocks are laid out on the disk. The default rotdelay value set by the and commands (see newfs(1M) and mkfs(1M)) is 0 milliseconds, causing file system blocks to be written and read consecutively. In general, this should be the optimal tun- ing, making the use of unnecessary. Options recognizes the following options and command-line arguments: Set the maximum number of contiguous blocks that will be laid out before forcing a rotational delay to maxcontig (see below). The default value is because most device drivers require one interrupt per disk transfer. For device drivers that can chain several buffers together in a single transfer, set maxcontig to the maximum chain length. rotdelay is the expected time (in milliseconds) to service a transfer completion interrupt and initiate a new transfer on the same disk. It is used to determine how much rotational spacing to place between successive blocks in a file. maxbpg specifies 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 fourth 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 cylin- der group, thus degrading access times for all files subsequently allocated in that cylinder group. The effect of this limit is to cause large 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. minfree specifies the percentage of space that is not available to normal users; i.e., the minimum free space threshold. The default value used is 10%. This value can be set to zero. If set to zero, throughput performance drops to as little as one-third of the efficiency expected when the threshold is set at 10%. Note that if minfree is raised above the current usage level, users cannot allocate files until enough files have been deleted to meet the new threshold requirement. Advanced read-ahead specifies whether the file system should use an advanced predictive read-ahead algorithm. The implementation requires more system resources in exchange for an advanced access pattern recognition. Patterns include forward sequential, backward sequential, forward strided, and backward strided. This value can be set to zero (disable) or one (enable). By default, a file system will have advanced read-ahead enabled when created. (visual) Display current values contained in the primary super-block to standard output. (all) Modify redundant super-blocks as well as the primary super-block as stipulated by the configuration options and arguments. special-device is the name of the file system to be tuned. It is either a block or character special file if the file system is not mounted, or a block special file if the file system is mounted. WARNINGS
Root file system tuning is normally done during initial system software installation. Tuning the root file system after installation has little useful effect because so many files have already been written. AUTHOR
was developed by the University of California, Berkeley. SEE ALSO
dumpfs(1M), mkfs(1M), newfs(1M). tunefs(1M)
