FSTRIM(8)						      System Manager's Manual							 FSTRIM(8)

NAME

       fstrim - discard unused blocks on a mounted filesystem

SYNOPSIS

       fstrim [-o offset] [-l length] [-m minimum-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  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/.

								     Nov 2010								 FSTRIM(8)