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_maxmaxphys.

			    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       -d rotdelay	    This parameter is obsolete as of the Solaris 10 release.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. However, up to a factor of three in throughput will be lost over the performance obtained at a  10%  thresh-
			    old.  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 fragmentation 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 5.11							    5 Dec 2003								tunefs(1M)