raid1 repair does not repair errors?

[Michael Tokarev <mjt@tls.msk.ru>]

Hello.

I've a raid1 array (composed of 4 drives, so it is a 4-fold
copy of data), and one of the drives has an unreadable (bad)
sector in the partition belonging to this array.

When I run md 'repair' action, it hits the error place, the
kernel clearly returns an error, but md does not do anything
with it.  For example:

Oct 21 18:43:55 mother kernel: [190018.073098] md: requested-resync of RAID array md1
Oct 21 18:43:55 mother kernel: [190018.093910] md: minimum _guaranteed_  speed: 1000 KB/sec/disk.
Oct 21 18:43:55 mother kernel: [190018.114765] md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for requested-resync.
Oct 21 18:43:55 mother kernel: [190018.136459] md: using 128k window, over a total of 2096064k.
Oct 21 18:45:11 mother kernel: [190094.091974] ata6.00: exception Emask 0x0 SAct 0xf SErr 0x0 action 0x0
Oct 21 18:45:11 mother kernel: [190094.114093] ata6.00: irq_stat 0x40000008
Oct 21 18:45:11 mother kernel: [190094.135906] ata6.00: failed command: READ FPDMA QUEUED
Oct 21 18:45:11 mother kernel: [190094.157710] ata6.00: cmd 60/00:00:00:3b:3e/04:00:00:00:00/40 tag 0 ncq 524288 in
Oct 21 18:45:11 mother kernel: [190094.157710]          res 41/40:00:29:3e:3e/00:00:00:00:00/40 Emask 0x409 (media error) <F>
Oct 21 18:45:11 mother kernel: [190094.202315] ata6.00: status: { DRDY ERR }
Oct 21 18:45:11 mother kernel: [190094.224517] ata6.00: error: { UNC }
Oct 21 18:45:11 mother kernel: [190094.248920] ata6.00: configured for UDMA/133
Oct 21 18:45:11 mother kernel: [190094.271003] sd 5:0:0:0: [sdc] Unhandled sense code
Oct 21 18:45:11 mother kernel: [190094.293044] sd 5:0:0:0: [sdc]
Oct 21 18:45:11 mother kernel: [190094.314654] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
Oct 21 18:45:11 mother kernel: [190094.336483] sd 5:0:0:0: [sdc]
Oct 21 18:45:11 mother kernel: [190094.357966] Sense Key : Medium Error [current] [descriptor]
Oct 21 18:45:11 mother kernel: [190094.379808] Descriptor sense data with sense descriptors (in hex):
Oct 21 18:45:11 mother kernel: [190094.402024]         72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00
Oct 21 18:45:11 mother kernel: [190094.424502]         00 3e 3e 29
Oct 21 18:45:11 mother kernel: [190094.446338] sd 5:0:0:0: [sdc]
Oct 21 18:45:11 mother kernel: [190094.467995] Add. Sense: Unrecovered read error - auto reallocate failed
Oct 21 18:45:11 mother kernel: [190094.490075] sd 5:0:0:0: [sdc] CDB:
Oct 21 18:45:11 mother kernel: [190094.511870] Read(10): 28 00 00 3e 3b 00 00 04 00 00
Oct 21 18:45:11 mother kernel: [190094.533829] end_request: I/O error, dev sdc, sector 4079145
Oct 21 18:45:11 mother kernel: [190094.555800] ata6: EH complete
Oct 21 18:45:22 mother kernel: [190105.602687] md: md1: requested-resync done.

There's no indication that raid code tried to re-write the bad spot,
and the bad block remains bad in the drive, so next read (direct from
the drive) return the same I/O error with the same kernel messages.

Shouldn't `repair' action re-write the problem place?

This is kernel 3.10.15.

Thank you!

/mjt