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 begin-
	      ning 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)