On 01/10/2011 12:26 AM, NeilBrown wrote:
> On Sun, 09 Jan 2011 23:48:05 +0100 Christian Schmidt <charlie@xxxxxxxxx>
> wrote:
>
>> Hi all,
>>
>> As the subject says, I'm wondering what issuing the "check" command to a
>> raid array does.
>
> May I suggest
> man 4 md
>
> Does that answer your question?
Yes, indeed. Thanks.
>> A possibly related question is: why did this member turn into "spare"
>> role? The system was fully functional and in daily use for about a year.
>> It was declared to be a four drive raid 5 with no spares. If I remember
>> level 5 correctly there is no single drive for the redundancy data to
>> avoid bottlenecks, right?
>
> One would need to see the history of the whole array, not just the current
> state of a single device, to be able to guess the reason for the current
> state.
>
> And yes: RAID5 distributes the parity blocks to avoid bottlenecks.
>
>>
>> alpha md # mdadm --examine --verbose /dev/sdh2
>> /dev/sdh2:
>> Magic : a92b4efc
>> Version : 1.2
>> Feature Map : 0x0
>> Array UUID : fa8fb033:6312742f:0524501d:5aa24a28
>> Name : sysresccd:1
>> Creation Time : Sat Jul 17 02:57:27 2010
>> Raid Level : raid5
>> Raid Devices : 4
>>
>> Avail Dev Size : 3904927887 (1862.01 GiB 1999.32 GB)
>> Array Size : 11714780160 (5586.04 GiB 5997.97 GB)
>> Used Dev Size : 3904926720 (1862.01 GiB 1999.32 GB)
>> Data Offset : 2048 sectors
>> Super Offset : 8 sectors
>> State : clean
>> Device UUID : 172eb49b:03e62242:614d7ed3:1fb25f65
>>
>> Update Time : Sun Jan 9 19:55:09 2011
>> Checksum : a991f168 - correct
>> Events : 34
>>
>> Layout : left-symmetric
>> Chunk Size : 512K
>>
>> Device Role : spare
>> Array State : AAAA ('A' == active, '.' == missing)
>>
>> Too bad that 1.2 superblocks don't contain the full array information
>> like 0.90 did.
>
> The extra information that 0.90 stored was not (and could not be) reliable.
>
> This device thinks that that the array is functioning correctly with no
> failed devices, and that this device is a spare - presumably a 5th device?
> It doesn't know the names of the other devices (and if it thought it did, it
> could easily be wrong as names changed). What do the other devices think of
> the state of the array?
[~]>mdadm -Q --detail /dev/md3
/dev/md3:
Version : 1.02
Creation Time : Sat Jul 17 02:57:27 2010
Raid Level : raid5
Array Size : 5857390080 (5586.04 GiB 5997.97 GB)
Used Dev Size : 1952463360 (1862.01 GiB 1999.32 GB)
Raid Devices : 4
Total Devices : 4
Persistence : Superblock is persistent
Update Time : Mon Jan 10 00:38:00 2011
State : clean, recovering
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 512K
Rebuild Status : 68% complete
Name : sysresccd:1
UUID : fa8fb033:6312742f:0524501d:5aa24a28
Events : 34
Number Major Minor RaidDevice State
0 8 34 0 active sync /dev/sdc2
1 8 50 1 active sync /dev/sdd2
2 8 82 2 active sync /dev/sdf2
4 8 114 3 active sync /dev/sdh2
So just "check" turns the array into rebuild mode and one of the drives
into a spare? That's unexpected.
Thanks,
Christian
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