While doing rsyncs of large archives from one RAID-1 btrfs filesystem to another RAID-1 btrfs filesystem: btrfs filesystem 1: sda + sdb (RAID-1), being copied to: btrfs filesystem 2: sdc + sdd (RAID-1) Server has 32 GB RAM I can observe the following: >From time to time, rsync "freezes", while there is high IO on only *one* of write drives. To reproduce: dd if=/dev/urandom of=/mnt/btrfs1/bigfile.img bs=1M count=10000; sync # cp should work, too, but won't show copy speed/progress rsync -a -v --progress /mnt/btrfs1/bigfile.img /mnt/btrfs2/ In another terminal, run iostat -m 1: 1) a few seconds of writes to only one RAID-1 member: Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn sdc 355.00 0.00 177.50 0 177 sdb 0.00 0.00 0.00 0 0 sdd 0.00 0.00 0.00 0 0 sda 0.00 0.00 0.00 0 0 2) then, a few seconds of writes to the other RAID-1 member: Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn sdc 0.00 0.00 0.00 0 0 sdb 0.00 0.00 0.00 0 0 sdd 351.00 0.00 175.50 0 175 sda 0.00 0.00 0.00 0 0 Is it optimal behaviour? With software RAID-1, I'm seeing writes to both devices at the same time. Also, what happens when the system crashes, and one drive has several hundred megabytes data more than the other one? -- Tomasz Chmielewski http://wpkg.org -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
