[Linux-cluster] GFS in a small cluster

Maciej Bogucki maciej.bogucki at artegence.com
Fri May 30 07:38:16 UTC 2008

> 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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