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.
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
sdb 910.89 13.46 18.77 1252768 1747442
New device was sda - so it's expected it wrote quite a lot of data
there.
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.
# btrfs filesystem show
Label: 'test-btrfs' uuid: 60f1759c-45f6-4484-9f60-66a4e9bbf2b6
Total devices 2 FS bytes used 1.19TB
devid 3 size 2.56TB used 1.19TB path /dev/sdb4
devid 4 size 2.56TB used 1.19TB path /dev/sda4
Btrfs v0.20-rc1-324-g650e656
--
Tomasz Chmielewski
http://wpkg.org
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