1FSTRIM(8)                    System Administration                   FSTRIM(8)
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NAME

6       fstrim - discard unused blocks on a mounted filesystem
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SYNOPSIS

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

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

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

73       Lukas Czerner <lczerner@redhat.com>
74       Karel Zak <kzak@redhat.com>
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SEE ALSO

77       mount(8)
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AVAILABILITY

80       The fstrim command is part of the util-linux package and  is  available
81       from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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85util-linux                       November 2010                       FSTRIM(8)