In addition to my previous "it does not happen here" comment, if someone is reading this thread, there are some other interesting details:
> When the compression is turned off, I am able to get the > maximum 500-600 mb/s write speed on this disk (raid array) > with minimal cpu usage. No details on whether it is a parity RAID or not. > btrfs device usage /mnt/arh-backup1/ > /dev/sda, ID: 2 > Device size: 21.83TiB > Device slack: 0.00B > Data,single: 9.29TiB > Metadata,single: 46.00GiB > System,single: 32.00MiB > Unallocated: 12.49TiB That's exactly 24TB of "Device size", of which around 45% are used, and the string "backup" may suggest that the content is backups, which may indicate a very fragmented freespace. Of course compression does not help with that, in my freshly created Btrfs volume I get as expected: soft# umount /mnt/sde3 soft# mount -t btrfs -o commit=10 /dev/sde3 /mnt/sde3 soft# /usr/bin/time dd iflag=fullblock if=/dev/sda6 of=/mnt/sde3/testfile bs=1M count=10000 conv=fsync 10000+0 records in 10000+0 records out 10485760000 bytes (10 GB) copied, 103.747 s, 101 MB/s 0.00user 11.56system 1:44.86elapsed 11%CPU (0avgtext+0avgdata 3072maxresident)k 20480672inputs+20498272outputs (1major+349minor)pagefaults 0swaps soft# filefrag /mnt/sde3/testfile /mnt/sde3/testfile: 11 extents found versus: soft# umount /mnt/sde3 soft# mount -t btrfs -o commit=10,compress=lzo,compress-force /dev/sde3 /mnt/sde3 soft# /usr/bin/time dd iflag=fullblock if=/dev/sda6 of=/mnt/sde3/testfile bs=1M count=10000 conv=fsync 10000+0 records in 10000+0 records out 10485760000 bytes (10 GB) copied, 109.051 s, 96.2 MB/s 0.02user 13.03system 1:49.49elapsed 11%CPU (0avgtext+0avgdata 3068maxresident)k 20494784inputs+20492320outputs (1major+347minor)pagefaults 0swaps soft# filefrag /mnt/sde3/testfile /mnt/sde3/testfile: 49287 extents found Most the latter extents are mercifully rather contiguous, their size is just limited by the compression code, here is an extract from 'filefrag -v' from around the middle: 24757: 1321888.. 1321919: 11339579.. 11339610: 32: 11339594: 24758: 1321920.. 1321951: 11339597.. 11339628: 32: 11339611: 24759: 1321952.. 1321983: 11339615.. 11339646: 32: 11339629: 24760: 1321984.. 1322015: 11339632.. 11339663: 32: 11339647: 24761: 1322016.. 1322047: 11339649.. 11339680: 32: 11339664: 24762: 1322048.. 1322079: 11339667.. 11339698: 32: 11339681: 24763: 1322080.. 1322111: 11339686.. 11339717: 32: 11339699: 24764: 1322112.. 1322143: 11339703.. 11339734: 32: 11339718: 24765: 1322144.. 1322175: 11339720.. 11339751: 32: 11339735: 24766: 1322176.. 1322207: 11339737.. 11339768: 32: 11339752: 24767: 1322208.. 1322239: 11339754.. 11339785: 32: 11339769: 24768: 1322240.. 1322271: 11339771.. 11339802: 32: 11339786: 24769: 1322272.. 1322303: 11339789.. 11339820: 32: 11339803: But again this is on a fresh empty Btrfs volume. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
