[Linux-cluster] Some experiences and questions concerning GFS vs. GPFS

Hansjoerg.Maurer at dlr.de Hansjoerg.Maurer at dlr.de
Thu Jan 6 12:16:19 UTC 2005


we are planing to implement a Linux Cluster Solution with shared SAN storage in Q2/2005.

We already tried RedHat GFS in a old test SAN environment, and it works great.

As an alternative solution we found a product called GPFS from IBM (gerneral parallel file system)

It seems to have some features, GFS does not have now, but according to the documentation, 
it seems to bee very complex and it seems to support only IBM Storage devices (FastT....).

The advantages seem to be
- filesystems up to 100 TB on IA32 (Blocksize up to 1MByte)
- syncronous replication of pools
- better scaling 
  If you have one RAID5 array in the SAN (lets call it RAID-A) and you add another RAID5 array
  (RAID-B) you can but them together, exceed the filesystem and reallocate the filesystem while it is online 
  to a stripeset over RAID-A AND RAID-B in order to get optimal performance.

The disadvantages seem to bee 
- the dependency on IBM Storage devices (especially for fencing)
- the complexity (fileaccess takes place over a userspace daemon, which caches data and stat information)
  This seems to be the reason they can achieve the file system size
- the integration of GFS into RHEL seems to be better of course... :-)

ok, now my questions 
What is the status of GFS for RHEL4 concerning the advantages of GPFS from above

- is it correct, that GFS filesystems in RHEL4 even on x86_64 can be very big (PByte) to? 
- will there be something similar like the reallocation of a stripe set over a newly created array in RHEL4 GFS?
- the possibility of syncronous mirroring is not so important in our special case...
- will the next stable version of GFS with the above features be available with initial Release of RHEL4 or 
  is there an other planed release date. We want to implement the SAN in Q2/2005, so that we can wait
  if some of the limitations of GFS will be negotiated until than.

And a final questions:
- has anybody experience with both products, so that he can tell me about advantages and disadvantages 
  (especially concerning performance). We will recieve a GPFS evaluation licence next week, but our
  old SAN storage hardware is not apropriate for performance tests, because it will be the bottleneck :-)

Sorry if this E-Mail is a bit off topic.
Sales persons are often showing you only the advantages of their product, 
and I hope that someone can help me with practical experiences.

If you think, that this is off topic, please answer directly.

Thank you very much




We will  


Dr.  Hansjoerg Maurer           | LAN- & System-Manager
Deutsches Zentrum               | DLR Oberpfaffenhofen
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