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Re: [Linux-cluster] GFS in a small cluster



The cluster, if it goes into production, will have to serve 'dynamic' files
to the webservers, these include images, videos and generic downloads. So
what will happen on the SAN is many reads, and relatively very few writes,
at the moment the read-write proportions on the NFS server are around 99%
reads vs 1% writes, the only writes that occur are users uploading a new
image, or one server creating some graphs.
No problem to GFS.
Not only the webservers will use this SAN, but also the database servers
will use it to read some files from it. I have been looking at different
filesystems to run on this SAN the suit my needs, and GFS is one of those,
but I have a few problems and questions.
Create two LUN on the array, one for database and the second for static files with two GFS fs on the top of it.


- Is locking really needed? There is no chance one webserver will try to
write to a file that is being written to by another file.
Yes, you need locking, if You have more than one serwer in the cluster.

- How about fencing? I'd rather have a corrupt filesystem than a corrupt
database, how silly that may sound, but I do not want the webservers be able
to switch off the (infinite more important) database servers, and all
servers can easily work without any problem without the share, they will
still serve most of the content, just not the user-uploaded images / videos
/ downloads.
Configure one ore more fencing method for the cluster and sleep well ;)


Is GFS the right FS for me or do I need to look to other (cluster aware)
filesystems?
Yes, but when You properly configure it(fe. configure/test fencing).

The other FS we looked at was OCFS2, but although it is a lot easier to set
up, and it works without any problems, it does have a limit of 32k
directories in one directory, something which we easily surpass on our
current shares (over 50k directories in one dir).
OCFS2 is similar to GFS, and it is for Oracle RAC environment. I suggest to use GFS, because it is more popular than OCFS2.
Anyway, is there a method to have gfs mounted without locking, but still be
cluster-aware (aka; the fs can be updated by other servers) and without
fencing?
Yes, but only on one node. Manual fencing is needed for production environment!

Best Regards
Maciej Bogucki




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