Re: Resize Raid5 devices

[Goswin von Brederlow <goswin-v-b@web.de>]

Ralf Müller <ralf@bj-ig.de> writes:

> Am 18.06.2009 um 10:27 schrieb Goswin von Brederlow:
>> Ralf Müller <ralf@bj-ig.de> writes:
>>
>>> After I added a forth 1.5TB disk to the array yesterday and  
>>> reshaped the
>>> former 3 disk raid5 to a 4 disk one, I wiped out the 300GB disk  
>>> raid5,
>>> set one of the 1.2TB partitions faulty, removed it from its raid,
>>> removed the 300GB partition and resized the former 1.2TB partition
>>> (in place) to 1.5TB. Now I added this partition to its raid.
>>>
>>> It has been recognized as a former member of this raid - so far so
>>> good - but for whatever reason the raid subsystem decided to start
>>> a complete recovery.
>>> So here my question:
>>>
>>> What went wrong and what do I have to do to avoid a full recovery for
>>> the next disk?
>>
>> I guess something wrote to your raid5 while the one disk was
>> removed.
>
> Thats possible - after re-add, the bitmap showed 2/275 pages as unclean.
>
>> When you added it back the event counter would differ and the
>> disk needs to be resynced completly. A bitmap would help limiting this
>> to the parts that have changed. Add an internal bitmap before you
>> remove the next disk.
>
> There is an internal write intent bitmap at the array:
> DatenGrab:/media # cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4] [raid1]
> md3 : active raid5 sdf1[3] sdi1[0] sdj1[4] sdh1[1]
>       3457099008 blocks super 1.2 level 5, 256k chunk, algorithm 2  
> [4/4] [UUUU]
>       bitmap: 0/275 pages [0KB], 2048KB chunk
>
> Do you have an idea why this bitmap has been ignored?

No idea.

MfG
        Goswin
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