[gpfsug-discuss] Checking a file-system for errors

[Uwe Falke]

Hm , mmfsck will  return not very reliable results in online mode, 
especially it will report many issues which are just due to the transient 
states in a files system in operation. 
It should however not find less issues than in off-line mode. 

mmrestripefs -c does not do any logical checks, it just checks for 
differences of multiple replicas of the same data/metadata.
File system errors can be caused by such discrepancies (if an odd/corrupt 
replica is used by the GPFS), but can also be caused (probably more 
likely) by logical errors / bugs when metadata were modified in the file 
system. In those cases, all the replicas are identical nevertheless 
corrupt (cannot be found by mmrestripefs)
 
So, mmrestripefs -c is like scrubbing for silent data corruption (on its 
own, it cannot decide which is the correct replica!), while mmfsck checks 
the filesystem structure for logical consistency. 
If the contents of the replicas of a data block differ, mmfsck won't see 
any problem (as long as the fs metadata are consistent), but mmrestripefs 
-c will. 

 
Mit freundlichen Grüßen / Kind regards

 
Dr. Uwe Falke
 
IT Specialist
High Performance Computing Services / Integrated Technology Services / 
Data Center Services
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From:   "Simon Thompson (IT Research Support)" <S.J.Thompson at bham.ac.uk>
To:     "gpfsug-discuss at spectrumscale.org" 
<gpfsug-discuss at spectrumscale.org>
Date:   10/11/2017 10:47 AM
Subject:        [gpfsug-discuss] Checking a file-system for errors
Sent by:        gpfsug-discuss-bounces at spectrumscale.org



I'm just wondering if anyone could share any views on checking a
file-system for errors.

For example, we could use mmfsck in online and offline mode. Does online
mode detect errors (but not fix) things that would be found in offline
mode?

And then were does mmrestripefs -c fit into this?

"-c
                  Scans the file system and compares replicas of
                  metadata and data for conflicts. When conflicts
                  are found, the -c option attempts to fix
                  the replicas.
"

Which sorta sounds like fix things in the file-system, so how does that
intersect (if at all) with mmfsck?

Thanks

Simon

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