[CentOS] [SOLVED] more software raid questions

Sat Oct 23 21:34:26 UTC 2010
fred smith <fredex at fcshome.stoneham.ma.us>

On Thu, Oct 21, 2010 at 11:03:27AM -0700, 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.

Nataraj, that worked fine, didn't need to --force it. Now I'm back to
having two devices in md0 and two in md1, and they're the RIGHT two! :)
Put the box in single-user mode to do the work, then after the array
finished resyncing, rebooted and it came up with the right two md devices.

I appreciate your tutoring me on this, you've been most helpful.

Thanks a bunch!

Oh, can you refer me to any good documentation on how to admin a
software raid system? One aimed for people, like me, who are 
computer literate, but have never trained as a sysadmin, and who
don't know much about RAID...

thanks again!

> 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.
> 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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---- Fred Smith -- fredex at fcshome.stoneham.ma.us -----------------------------
               But God demonstrates his own love for us in this: 
                         While we were still sinners, 
                              Christ died for us.
------------------------------- Romans 5:8 (niv) ------------------------------