I have a btrfs filesystem (2.6.39) which is mounted, but otherwise, not used:
# lsof -n|grep /mnt/btrfs # I noticed that whenever I do "sync", btrfs will write for around 6.5s and write 13 MB (see below). If I do a "while true; do sync; done", there will be constant writes to btrfs filesystem (again - with no userspace program accessing btrfs). When it happens, "btrfs-submit-0" is in "D" state. What are these writes? I didn't notice anything like this with other filesystems. $ iostat -t -k 1 sdb4|grep sdb4 Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn sdb4 320.00 0.00 1660.00 0 1660 sdb4 419.00 0.00 1720.00 0 1720 sdb4 291.00 0.00 1224.00 0 1224 sdb4 417.00 0.00 1736.00 0 1736 sdb4 609.00 0.00 2628.00 0 2628 sdb4 350.00 0.00 1452.00 0 1452 sdb4 606.00 0.00 2620.00 0 2620 sdb4 281.00 0.00 1516.00 0 1516 sdb4 352.00 0.00 1472.00 0 1472 sdb4 384.00 0.00 1584.00 0 1584 sdb4 533.00 0.00 2232.00 0 2232 sdb4 640.00 0.00 2660.00 0 2660 When btrfs is mounted with "compress" flag, there will be also reads when doing a similar operation. See MB_wrtn before/after the sync: $ iostat -t -m sdb4 Linux 2.6.39-020639-generic (dom) 05/21/2011 _x86_64_ (8 CPU) 05/21/2011 02:45:46 PM avg-cpu: %user %nice %system %iowait %steal %idle 2.47 0.01 1.25 8.01 0.00 88.26 Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn sdb4 127.39 0.92 1.94 94207 199343 $ time sync real 0m6.808s user 0m0.000s sys 0m0.110s $ iostat -t -m sdb4 Linux 2.6.39-020639-generic (dom) 05/21/2011 _x86_64_ (8 CPU) 05/21/2011 02:46:02 PM avg-cpu: %user %nice %system %iowait %steal %idle 2.47 0.01 1.25 8.01 0.00 88.26 Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn sdb4 127.40 0.92 1.94 94207 199356 $ time sync real 0m6.628s user 0m0.000s sys 0m0.110s $ iostat -t -m sdb4 Linux 2.6.39-020639-generic (dom) 05/21/2011 _x86_64_ (8 CPU) 05/21/2011 02:46:55 PM avg-cpu: %user %nice %system %iowait %steal %idle 2.47 0.01 1.25 8.01 0.00 88.27 Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn sdb4 127.37 0.92 1.94 94207 199369 -- Tomasz Chmielewski http://wpkg.org -- 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