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fstrim(8) [debian man page]

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)

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FALLOCATE(1)							   User Commands						      FALLOCATE(1)

NAME
fallocate - preallocate or deallocate space to a file SYNOPSIS
fallocate [-c|-p|-z] [-o offset] -l length [-n] filename fallocate -d [-o offset] [-l length] filename fallocate -x [-o offset] -l length filename DESCRIPTION
fallocate is used to manipulate the allocated disk space for a file, either to deallocate or preallocate it. For filesystems which support the fallocate system call, preallocation is done quickly by allocating blocks and marking them as uninitialized, requiring no IO to the data blocks. This is much faster than creating a file by filling it with zeroes. The exit code returned by fallocate is 0 on success and 1 on failure. OPTIONS
The length and offset arguments may be followed by the multiplicative suffixes KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g., "K" has the same meaning as "KiB") or the suffixes KB (=1000), MB (=1000*1000), and so on for GB, TB, PB, EB, ZB and YB. The options --collapse-range, --dig-holes, --punch-hole and --zero-range are mutually exclusive. -c, --collapse-range Removes a byte range from a file, without leaving a hole. The byte range to be collapsed starts at offset and continues for length bytes. At the completion of the operation, the contents of the file starting at the location offset+length will be appended at the location offset, and the file will be length bytes smaller. The option --keep-size may not be specified for the collapse-range operation. Available since Linux 3.15 for ext4 (only for extent-based files) and XFS. -d, --dig-holes Detect and dig holes. This makes the file sparse in-place, without using extra disk space. The minimum size of the hole depends on filesystem I/O block size (usually 4096 bytes). Also, when using this option, --keep-size is implied. If no range is specified by --offset and --length, then the entire file is analyzed for holes. You can think of this option as doing a "cp --sparse" and then renaming the destination file to the original, without the need for extra disk space. See --punch-hole for a list of supported filesystems. -i, --insert-range Insert a hole of length bytes from offset, shifting existing data. -l, --length length Specifies the length of the range, in bytes. -n, --keep-size Do not modify the apparent length of the file. This may effectively allocate blocks past EOF, which can be removed with a truncate. -o, --offset offset Specifies the beginning offset of the range, in bytes. -p, --punch-hole Deallocates space (i.e., creates a hole) in the byte range starting at offset and continuing for length bytes. Within the specified range, partial filesystem blocks are zeroed, and whole filesystem blocks are removed from the file. After a successful call, subse- quent reads from this range will return zeroes. This option may not be specified at the same time as the --zero-range option. Also, when using this option, --keep-size is implied. Supported for XFS (since Linux 2.6.38), ext4 (since Linux 3.0), Btrfs (since Linux 3.7) and tmpfs (since Linux 3.5). -v, --verbose Enable verbose mode. -x, --posix Enable POSIX operation mode. In that mode allocation operation always completes, but it may take longer time when fast allocation is not supported by the underlying filesystem. -z, --zero-range Zeroes space in the byte range starting at offset and continuing for length bytes. Within the specified range, blocks are preallo- cated for the regions that span the holes in the file. After a successful call, subsequent reads from this range will return zeroes. Zeroing is done within the filesystem preferably by converting the range into unwritten extents. This approach means that the spec- ified range will not be physically zeroed out on the device (except for partial blocks at the either end of the range), and I/O is (otherwise) required only to update metadata. Option --keep-size can be specified to prevent file length modification. Available since Linux 3.14 for ext4 (only for extent-based files) and XFS. -V, --version Display version information and exit. -h, --help Display help text and exit. AUTHORS
Eric Sandeen <sandeen@redhat.com> Karel Zak <kzak@redhat.com> SEE ALSO
truncate(1), fallocate(2), posix_fallocate(3) AVAILABILITY
The fallocate command is part of the util-linux package and is available from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils /util-linux/>. util-linux April 2014 FALLOCATE(1)
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