Re: [Moosefs-users] Question about MooseFS metadata distribution/recovery

[René P. <ly...@lu...>]

On Dec 12, 2011 at 1554 -0800, wkmail appeared and said:
> On 12/12/2011 3:36 PM, René Pfeiffer wrote:
> > …
> > The biggest problem is that we cannot figure out what the RAID controller
> > exactly did to the file system of the master server, and we haven't found
> > any traces of a more recent metadata file. The metalogger system had no
> > problem, but can it be that the metalogger was/is out of sync due to the
> > silent file system corruption on the master system?
> 
> That is a question for the devs, but early in our MFS testing with 
> essentially throwaway kit, we had a master fail with a broken raid. In 
> that case the underlying disk system had been essentially readonly for a 
> few days and no recent data was in /usr/local/var/mfs.
> 
> However, the metalogger DID have accurate information and we simply 
> recovered using that data using the restore process and then copying 
> over metadata file to the now fixed master. Except for the 'on the fly 
> files' lost when the damm thing crashed, no other data was lost, 
> including files that had been received and written to chunkserver during 
> the time the disk subsystem was out of order.
> 
> So my guess is that the metaloggers get their info from the masters 
> memory, not from a file on the master.

Ok, this might be the reason then, because the master went down hard two
times (first time 21 October, second time 9 December) because the RAID
controller totally locked the system. I assume this could
explain some missing metadata.

> But that is something that should be confirmed by the devs.

Thanks,
René.

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