[NTLUG:Discuss] NFS Synchronization

[Chris Cox]

On Thu, 2010-05-20 at 14:08 -0700, George Lass wrote:
> I need to set up a pair of NFS servers that need to be synchronized and am wondering if rsync is the right way to do it?  The primary use of the pair of servers is for recording and playback of phone messages stored in .wav files.  The only "gotcha" is that any particular recording will originally be written (recorded) randomly to one of the servers or the other, while read (playback) requests can be made to either server.  Thus within just a minute or 2, the file must be propagated from one server to the other.  It should be assumed that the directory structures where the .wav files reside are identical on both machines.
> 
> Thanks in advance for any advice on this,

Have you considered a clustered filesystem (e.g. GFS2 or ocfs2)?

Regardless, with independent NFS, there's a cache consistency issue
possibly.  Why the need for TWO NFS's??  You could have a HA NFS on top
of GFS2 today pretty easily (that means that NFS is reliable, but ONLY
one up and exporting at a time... and I'm not totally sure that there
won't be some weird client caching issues on failover).

Rsync takes time to look at things and then is lightning fast at getting
stuff across.  The more that has to be analyzed, the more likely that
rsync won't keep up.  So... it MAY be possible just because you have
some "gap" time.... but not sure if you can guarantee anything.

You could build your NFS areas on top of a drdb maybe... I think that's
a pretty big risk though.... again, NFS doesn't coordinate across
multiple NFS's, so there's still that stupid consistency issue with
regards to what is seen.