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 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/.
util-linux November 2010 FSTRIM(8)