tunefs - tune an existing UFS file system


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


     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.


     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 calcu-
           lated 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           This parameter is obsolete. 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 contigu-
           ous  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% 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 fragmentation on the  disk.  The
           default is time.

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


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


     See attributes(5) for descriptions of the  following  attri-

    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    | Availability                | SUNWcsu                     |


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

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