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Linux 2.6 - man page for fstrim (linux section 8)

FSTRIM(8)										FSTRIM(8)

       fstrim - discard unused blocks on a mounted filesystem

       fstrim [-o offset] [-l length] [-m minimum-extent] [-v] mountpoint

       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

       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.

       The offset, length, and minimum-free-extent arguments may be followed by binary (2^N) suf-
       fixes 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 repeat-

	      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  set-
	      up, etc.	These reductions would not be reflected in fstrim_range.len (the --length

       Lukas Czerner <lczerner@redhat.com>
       Karel Zak <kzak@redhat.com>


       The fstrim command is part of the util-linux package and is available from  ftp://ftp.ker-

					     Nov 2010					FSTRIM(8)

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