Dear btrfs community,

I have the following setup:

# btrfs fi show /home
Label: none  uuid: 865f8cf9-27be-41a0-85a4-6cb4d1658ce3
	Total devices 3 FS bytes used 55.68GiB
	devid    1 size 52.91GiB used 0.00B path /dev/sdd2
	devid    2 size 232.89GiB used 59.03GiB path /dev/sda
	devid    3 size 111.79GiB used 59.03GiB path /dev/sdc1

btrfs volume was created in raid1 mode both for data and metadata and mounted
with compress=lzo option.

Unfortunately, two drives (sda and sdc1) started to fail at the same time. This
leads to system crash if I start the system in runlevel 3 (see crash1.log).

After I have started the system in single mode, volume can be mounted in rw
mode and I can write some data into it. Unfortunately when I tried to read
a certain file, the system crashed (see crash2.log).

I have started scrub on the volume and here is the report:

# btrfs scrub status /home
scrub status for 865f8cf9-27be-41a0-85a4-6cb4d1658ce3
	scrub started at Tue Apr 12 20:39:20 2016 and finished after 02:40:09
	total bytes scrubbed: 55.68GiB with 1767 errors
	error details: verify=175 csum=1592
	corrected errors: 1110, uncorrectable errors: 657, unverified errors: 0

Obviously, some data is lost. However due to above crash, I cannot just copy
the data from the volume. I would assume that I still can access the data, but
the files for which data is lost, should result I/O error (I would then recover
them from my backup).

I have decided to attach another drive and remove failing devices one-by-one.
However that does not work:

# btrfs dev delete /dev/sda /home
[  168.680057] ata3.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
[  168.684236] ata3.00: BMDMA stat 0x25
[  168.688464] ata3.00: failed command: READ DMA
[  168.692681] ata3.00: cmd c8/00:08:68:4b:84/00:00:00:00:00/e7 tag 0 dma 4096 in
[  168.692681]          res 51/40:08:68:4b:84/40:08:07:00:00/e7 Emask 0x9 (media error)
[  168.701281] ata3.00: status: { DRDY ERR }
[  168.705600] ata3.00: error: { UNC }
[  168.724446] blk_update_request: I/O error, dev sda, sector 126110568
[  168.728860] BTRFS error (device sdc1): bdev /dev/sda errs: wr 0, rd 43, flush 0, corrupt 0, gen 0
[  172.824043] ata3.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
[  172.828651] ata3.00: BMDMA stat 0x25
[  172.833281] ata3.00: failed command: READ DMA
[  172.837876] ata3.00: cmd c8/00:08:50:4b:84/00:00:00:00:00/e7 tag 0 dma 4096 in
[  172.837876]          res 51/40:08:50:4b:84/40:08:07:00:00/e7 Emask 0x9 (media error)
[  172.847296] ata3.00: status: { DRDY ERR }
[  172.852054] ata3.00: error: { UNC }
[  172.872404] blk_update_request: I/O error, dev sda, sector 126110544
[  172.877241] BTRFS error (device sdc1): bdev /dev/sda errs: wr 0, rd 44, flush 0, corrupt 0, gen 0
ERROR: error removing device '/dev/sda': Input/output error

The same happens when I try to delete /dev/sdc1 from the volume. Is there any
btrfs "force" option so that btrfs balances only chunks that are accessible? I
can potentially physically disconnect /dev/sda, but the loss will be greater
I believe.

How can I proceed except btrfs restore?

During scrub operation the following was recorded in the logs:

[Tue Apr 12 23:10:20 2016] BTRFS warning (device sdc1): checksum error at logical 126952947712 on dev /dev/sdc1, sector 126150176, root 258, inode 879324, offset 308256768, length 4096, links 1 (path: lib/mysql/ibdata1)

If I collect all the messages like this, will it give a full picture of damaged files?

Many thanks in advance.

P.S. Linux kernel v4.4.2, btrfs-progs v4.4.

-- 
With best regards,
Dmitry