Blog/Btrfs defrag with progress output
Btrfs Filesystem Defrag[edit | edit source]
The Copy-on-Write nature of Btrfs can lead to high amounts of fragmentation in files that are written or update in small bits. This is because for each new write, Btrfs have to write the data to a new location. Especially on spinning HDD's, this can lead to extra seeks and slowness.
btrfs filesystem defragment can be used to defragment files to make the more continuous, thus improving read speeds. Defrag can also be used to apply compression to files, reducing their space usage and increase read/write speeds.
Read more about defragmentation on Btrfs on Btrfs/Defrag
# btrfs filesystem defragment --help
usage: btrfs filesystem defragment [options] <file>|<dir> [<file>|<dir>...]
Defragment a file or a directory
-r defragment files recursively
-c[zlib,lzo,zstd] compress the file while defragmenting, optional parameter (no space in between)
-f flush data to disk immediately after defragmenting
-s start defragment only from byte onward
-l len defragment only up to len bytes
-t size target extent size hint (default: 32M)
--step SIZE process the range in given steps, flush after each one
-v deprecated, alias for global -v option
Global options:
-v
Defrag in steps, with progress output[edit | edit source]
Btrfs-progs v6.6 came with a new feature, --step, which helps when defragmentig very large files.
Lets consider the following VM image file:
# compsize haikur1beta3-2.img
Processed 1 file, 7905 regular extents (7905 refs), 0 inline. Type Perc Disk Usage Uncompressed Referenced TOTAL 98% 3.6G 3.6G 3.6G none 100% 3.5G 3.5G 3.5G zstd 40% 25M 63M 63M
Combining -vv (verbose) with --step, we get a nice progress report while defragmenting the file.
The step size can be between 256KiB and 4GiB.
# btrfs -vv fi defrag --step 1G haikur1beta3-2.img
haikur1beta3-2.img defrag range step: start=0 len=1073741824 step=1073741824 defrag range step: start=1073741824 len=1073741824 step=1073741824 defrag range step: start=2147483648 len=1073741824 step=1073741824 defrag range step: start=3221225472 len=1073741824 step=1073741824
Compsize shows we have reduced the amount of fragmentation quite a bit.
# compsize haikur1beta3-2.img
Processed 1 file, 641 regular extents (641 refs), 0 inline. Type Perc Disk Usage Uncompressed Referenced TOTAL 98% 3.6G 3.6G 3.6G none 100% 3.5G 3.5G 3.5G zstd 40% 25M 63M 63M
