[CentOS] more software raid questions

Thu Oct 21 18:07:16 UTC 2010
Nataraj <incoming-centos at rjl.com>

Nataraj wrote:
> fred smith wrote:
>> Thanks for the additional information.
>> I'll try backing up everything this weekend then will take a stab at it.
>> someone said earlier that the differing raid superblocks were probably
>> the cause of the misassignment in the first place. but I have no clue
>> how the superblocks could have become messed up, can any of you comment
>> on that? willl I need to hack at that issue, too, before I can succeed?
>> thanks again!
>>> Nataraj
> I would first try adding the drives back in with:
> mdadm /dev/mdN -a /dev/sdXn
> Again, this is after having stopped the bogus md arrays.
> If that doesn't work, I would try assemble with a --force option, which 
> might be a little more dangerous than the hot add, but probably not 
> much. I can say that when I have a drive fall out of an array I am 
> always able to add it back with the first command (-a). As I mentioned, 
> I do have bitmaps on all my arrays, but you can't change that until you 
> rebuild the raidset.
Note, that if you need to use assemble --force, you must stop the array 
first and know exactly which drives you want to assemble the array with.
> I believe these comands will take care of everything. You shouldn't have 
> to do any diddling of the superblocks at a low level, and if the problem 
> is that bad, you might be best to backup and recreate the whole array or 
> engage the services of someone who knows how to muck with the data 
> structures on the disk. I've never had to use anything other than mdadm 
> to manage my raid arrays and I've never lost data with linux software 
> raid in the 10 or more years that I've been using it. I've found it to 
> be quite robust. Backing up is just a precaution that is a good idea for 
> anyone to take if they care about their data.
> If these problems reoccur on a regular basis, you could have a bad 
> drive, a power supply problem or a cabling problem. Assuming your drives 
> are attached to SATA, SCSI or SAS controller, you can use smartctl to 
> check the drives and see if they are getting errors or other faults. 
> smartctl will not work with USB or firefire attached drives.
> Nataraj
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