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 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.
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,
−−helpPrint help and exit.
−o,
−−offset offsetByte 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 lengthNumber 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-extentMinimum 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,
−−verboseVerbose 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).