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Linux kernel software RAID mdadm: It Really Works!!!
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Lupin_the_3rd
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Joined: 03 Apr 2005
Posts: 168

PostPosted: Sat Dec 29, 2012 7:14 pm    Post subject: Linux kernel software RAID mdadm: It Really Works!!! Reply with quote

No questions or problems here, just wanted to post the kernel messages from a recent drive failure in my RAID-1 mirror. Everything worked exactly as it should, in fact, I didn't even realize a drive had failed until I ran `dmesg` to see the kernel messages as part of my routine system check. This is on my DEC Alpha workstation.

One thing to take away from this, is the benefit that Linux kernel software RAID provides - it protects not only against a complete drive failure - but also against bad sectors - if a sector on one drive becomes unreadable, it recovers the data from the other RAID member(s)! With a single drive (i.e. without RAID) you will lose the contents of any bad sectors, resulting in data corruption.

Anyhow, enough rambling, here's the log messages I found interesting. You can see it performing sector redirection, and then eventually booting the failed drive out of the array. We can all read about the theory of how it's supposed to work, but actually seeing it work is far more interesting:

end_request: I/O error, dev sdb, sector 29367344
md/raid1:md0: sdb1: rescheduling sector 29365296
md/raid1:md0: redirecting sector 29365336 to other mirror: sdc1
md/raid1:md0: redirecting sector 29365328 to other mirror: sdc1
md/raid1:md0: redirecting sector 29365320 to other mirror: sdc1
md/raid1:md0: redirecting sector 29365312 to other mirror: sdc1
md/raid1:md0: redirecting sector 29365304 to other mirror: sdc1
md/raid1:md0: redirecting sector 29365296 to other mirror: sdc1
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Read(10): 28 00 01 c0 1e 58 00 00 08 00
end_request: I/O error, dev sdb, sector 29367896
md/raid1:md0: sdb1: rescheduling sector 29365848
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Read(10): 28 00 01 c0 1e 50 00 00 08 00
end_request: I/O error, dev sdb, sector 29367888
md/raid1:md0: sdb1: rescheduling sector 29365840
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Read(10): 28 00 01 c0 1e 48 00 00 08 00
end_request: I/O error, dev sdb, sector 29367880
md/raid1:md0: sdb1: rescheduling sector 29365832
md/raid1:md0: redirecting sector 29365848 to other mirror: sdc1
md/raid1:md0: redirecting sector 29365840 to other mirror: sdc1
md/raid1:md0: redirecting sector 29365832 to other mirror: sdc1
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Read(10): 28 00 01 c0 3b c0 00 00 08 00
end_request: I/O error, dev sdb, sector 29375424
md/raid1:md0: sdb1: rescheduling sector 29373376
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Read(10): 28 00 01 c0 3b a8 00 00 08 00
end_request: I/O error, dev sdb, sector 29375400
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Read(10): 28 00 01 c0 3b a0 00 00 08 00
end_request: I/O error, dev sdb, sector 29375392
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Read(10): 28 00 01 c0 3b 98 00 00 08 00
end_request: I/O error, dev sdb, sector 29375384
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Read(10): 28 00 01 c0 3b 90 00 00 08 00
end_request: I/O error, dev sdb, sector 29375376
md/raid1:md0: redirecting sector 29373376 to other mirror: sdb1
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Read(10): 28 00 01 c0 4d c8 00 00 08 00
end_request: I/O error, dev sdb, sector 29380040
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Write(10): 2a 00 00 80 27 60 00 00 08 00
end_request: I/O error, dev sdb, sector 8398688
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Write(10): 2a 00 00 80 0b e8 00 00 08 00
end_request: I/O error, dev sdb, sector 8391656
sd 1:0:1:0: [sdb] Unhandled error code
sd 1:0:1:0: [sdb]
Result: hostbyte=DID_SOFT_ERROR driverbyte=DRIVER_OK
sd 1:0:1:0: [sdb] CDB:
Write(10): 2a 00 00 80 08 80 00 00 10 00
end_request: I/O error, dev sdb, sector 8390784
md/raid1:md0: Disk failure on sdb1, disabling device.
md/raid1:md0: Operation continuing on 1 devices.
RAID1 conf printout:
--- wd:1 rd:2
disk 0, wo:0, o:1, dev:sdc1
disk 1, wo:1, o:0, dev:sdb1
RAID1 conf printout:
--- wd:1 rd:2
disk 0, wo:0, o:1, dev:sdc1
_________________
Compaq XP1000 Alpha EV67 667Mhz w/ 2GB ECC
32bit PCI: ATI Radeon 9100 (DRI works!)
32bit PCI: Generic Firewire 400 card
64bit PCI: BCM5703 Gig-E (Compaq NC7771)
64bit PCI: Sil3124 SATA w/ mdadm RAID1 (pair of WD VelociRaptors)


Last edited by Lupin_the_3rd on Sat Dec 29, 2012 7:17 pm; edited 1 time in total
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frostschutz
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Joined: 22 Feb 2005
Posts: 2966
Location: Germany

PostPosted: Sat Dec 29, 2012 7:17 pm    Post subject: Re: Linux kernel software RAID mdadm: It Really Works!!! Reply with quote

Lupin_the_3rd wrote:
I didn't even realize a drive had failed until I ran `dmesg` to see the kernel messages as part of my routine system check.


You should set up mdadm and smartmond to send you mail when anything happens to any drive.
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