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 binary (2^N) suffixes KiB, MiB,
       GiB, TiB, PiB and EiB (the "iB" is optional, e.g. "K" has the same meaning as "KiB")  or  decimal  (10^N)
       suffixes KB, MB, GB, PB and EB.

       -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@redhat.com>
       Karel Zak <kzak@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)