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FSTRIM(8)                    System Administration                   FSTRIM(8)

NAME
       fstrim - discard unused blocks on a mounted filesystem
SYNOPSIS
       fstrim [-o offset] [-l length] [-m minimum-free-extent] [-v] mountpoint

DESCRIPTION
       fstrim  is  used  on a mounted filesystem to discard (or "trim") blocks
       which are not in use by the filesystem.  This is useful for solid-state
       drives (SSDs) and thinly-provisioned storage.
       By  default,  fstrim  will discard all unused blocks in the filesystem.
       Options may be used to modify this behavior based on range or size,  as
       explained below.
       The  mountpoint  argument  is  the  pathname of the directory where the
       filesystem is mounted.

OPTIONS
       The offset, length, and minimum-free-extent arguments may  be  followed
       by  the  multiplicative suffixes KiB=1024, MiB=1024*1024, and so on for
       GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g. "K" has the
       same meaning as "KiB") or the suffixes KB=1000, MB=1000*1000, and so on
       for GB, TB, PB, EB, ZB and YB.
       -h, --help
              Print help and exit.
       -o, --offset offset
              Byte offset in filesystem from which to begin searching for free
              blocks  to  discard.   Default  value  is  zero, starting at the
              beginning of the filesystem.
       -l, --length length
              Number of bytes after starting point to search for  free  blocks
              to  discard.  If the specified value extends past the end of the
              filesystem, fstrim will stop at the  filesystem  size  boundary.
              Default value extends to the end of the filesystem.
       -m, --minimum minimum-free-extent
              Minimum  contiguous free range to discard, in bytes. (This value
              is internally rounded up to a multiple of the  filesystem  block
              size).   Free  ranges  smaller  than  this  will be ignored.  By
              increasing this value, the fstrim operation will  complete  more
              quickly   for   filesystems  with  badly  fragmented  freespace,
              although not all blocks will be  discarded.   Default  value  is
              zero, discard every free block.
       -v, --verbose
              Verbose  execution. When specified fstrim will output the number
              of bytes passed from the filesystem down the block stack to  the
              device  for  potential discard. This number is a maximum discard
              amount from the storage  device's  perspective,  because  FITRIM
              ioctl  called  repeated  will  keep sending the same sectors for
              discard repeatedly.
              fstrim will report the same potential discard bytes  each  time,
              but  only sectors which had been written to between the discards
              would actually be discarded by the storage device.  Further, the
              kernel  block  layer  reserves  the  right to adjust the discard
              ranges to fit raid stripe geometry, non-trim capable devices  in
              a  LVM  setup,  etc.  These reductions would not be reflected in
              fstrim_range.len (the --length option).

AUTHOR
       Lukas Czerner <lczerner AT redhat.com>
       Karel Zak <kzak AT redhat.com>
SEE ALSO
       mount(8)
AVAILABILITY
       The fstrim command is part of the util-linux package and  is  available
       from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

util-linux                       November 2010                       FSTRIM(8)