On Aug 29, 2013, at 1:01 PM, Tomasz Chmielewski <tch@xxxxxxxxxxx> wrote: > So I've removed a missing device, which took some time: > > # time btrfs device delete missing /home > > real 1512m33.763s > user 0m0.000s > sys 121m37.740s > > OK, it needs time, fine. 25 hours seems like a long time … > And shifted quite large amounts of data: > > Device: tps MB_read/s MB_wrtn/s MB_read MB_wrtn > sda 347.00 0.37 16.24 34050 1512249 … for ~1.5TB. > > But why did it write so much on sdb (even more than on sda)? With > software RAID-1, when replacing a failed device, the amount of reads > from one drive is equal to the writes on the other drive; there is no > writing on the healthy drive. During the balance, chunks are read and re-written normally. Normal for raid1 means it will write two copies of each read chunk, therefore it writes to both devices. I don't know if it's possible, or planned, to optimize out the (seemingly) redundant write to the device that already has a legitimate copy. Chris Murphy-- 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
