tunefs(1M)						  System Administration Commands						tunefs(1M)

NAME

       tunefs - tune an existing UFS file system

SYNOPSIS

       tunefs [-a maxcontig] [-d rotdelay] [-e maxbpg] [-m minfree] [-o space | time]  special | filesystem

DESCRIPTION

       tunefs  is  designed  to change the dynamic parameters of a file system that affect the layout policies. When using tunefs with filesystem,
       filesystem must be in /etc/vfstab. The parameters that can be changed are indicated by the options given below.

OPTIONS

       The following options are supported:

       -a maxcontig

	   The maximum number of logical blocks, belonging to one file, that is allocated contiguously. The default is calculated as follows:

	   maxcontig = disk drive maximum transfer size / disk block size

	   If the disk drive's maximum transfer size cannot be determined, the default value for maxcontig is calculated from kernel parameters as
	   follows:

	   If  maxphys is less than ufs_maxmaxphys, which is 1 Mbyte, then maxcontig is set to maxphys. Otherwise, maxcontig is set to ufs_maxmax-
	   phys.

	   You can set maxcontig to any positive integer value.

	   The actual value will be the lesser of what has been specified and what the hardware supports.

       -d rotdelay

	   This parameter is obsolete as of the Solaris 10 release. The value is always set to 0, regardless of the input value.

       -e maxbpg

	   Indicates the maximum number of contiguous logical blocks any single file can allocate from a cylinder group before	it  is	forced	to
	   begin  allocating  blocks from another cylinder group. Typically this value is set to approximately one quarter of the total contiguous
	   logical 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.

       -m minfree

	   Specifies the minimum free space threshold, or the percentage of space held back from normal users. This value can be set  to  0.  How-
	   ever, up to a factor of three in throughput will be lost over the performance obtained at a 10% threshold. Note: 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.

       -o space|time

	   The	file system can either be instructed to try to minimize the time spent allocating blocks, or to try to minimize the space fragmen-
	   tation on the disk. The default is time.

	   Generally, you should optimize for time unless the file system is over 90% full.

USAGE

       See largefile(5) for the description of the behavior of tunefs when encountering files greater than or equal to 2 Gbyte ( 2**31 bytes).

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       mkfs_ufs(1M), newfs(1M), attributes(5), largefile(5)

SunOS 5.10							    5 Dec 2003								tunefs(1M)