High availability email server...

Dave McMurtrie dave64 at andrew.cmu.edu
Tue Aug 1 08:41:50 EDT 2006

Daniel Eckl wrote:

> Hi Scott!
> Your statements cannot be correct by logical reasons.
> While on file locking level you are fully right, cyrus heavily depends 
> on critical database access where you need application level database 
> locking.
> As only one master process can lock the database, a second one either 
> cannot lock the database or just crashes it with simultaneous write 
> access. I didn't try it by myself for obvious reasons...
> If that didn't occur to you, then you had incredible luck, that there 
> was no situation where both processes wanted to change the same db 
> file simultaneously.

Hi Daniel,

Scott is not just lucky, he's using clustering technology that works.  
When using a cluster filesystem that works, the locking semantics across 
cluster nodes will be the same as those on a single node filesystem.  
What you say above is simply not correct.

University of Pittsburgh is also running a 4-node active/active cluster 
using Veritas Cluster Filesystem and it works very well.  The 
performance is incredible, and as Scott pointed out you don't need the 
complexity of murder or application-level replication.  Using a cluster 
instead of Cyrus murder gives you both scalability and redundancy.  The 
big tradeoff is that Veritas Cluster Filesystem costs money, while Cyrus 
does not.



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