Clustering and replication

[Simon Matter]

> On Mon, Jan 29, 2007 at 04:14:33PM -0800, Tom Samplonius wrote:
>>
>> ----- "Simon Matter" <simon.matter at invoca.ch> wrote:
>> >
>> > Believe it or not, it works and has been confirmed by several peoples
>> on
>> > the list using different shared filesystems (VeritasFS and Tru64 comes
>> to
>> > mind). In one thing you are right, it doesn't work with BerkeleyDB.
>> > Just switch all your BDB's to skiplist and it works. This has really
>> been
>> > discussed on the list again and again and isn't it nice to know that
>> > clustering cyrus that way works?
>>
>>   Yes, useful.  But the original poster wanted to combine Cyrus
>>   application replication with a cluster filesystem (GFS
>>   specifically).  It seems pretty unusual to combine both.  GFS has a
>>   lot of locking overhead of writing, and e-mail storage is pretty
>>   write intensive.  And Cyrus replication can have its own performance
>>   issues (slow replication that never catches up).  Why do both at the
>>   same time?
>
> The reason to use a clustering FS: if it works, it is very simple. Each
> node can be more or less identical. And, therefore, more or less
> redundant. And the system is scalable (just add a node), to the point
> where the GFS locking overhead begins to be the bottleneck. And HA is
> simple: if you want to do maintenance a node, just get it offline -
> nobody'll notice.
>
> The reason to use replication: The "master" cluster has but one
> filesystem. Of course it's on a SAN, RAID, blah. But if the SAN fails -
> such a thing happened a couple years ago, even SANs fail - we lose all
> mail received since last backup. Not nice. (But if combining these two
> really result in severe performance losses, we might have to
> reconsider.)
>
>>   And GFS 6.1 (current version) has some issues with large directories:
>>
>> https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=214239
>
> This might be a problem, since we have some users that really have 10000
> messages in their INBOX. Although it seems that Cyrus itself cannot cope
> with this either... in our current, non-clustering setup. But then, it's
> an old version.

Interesting, I have some folders with ~100'000 messages and cyrus handles
it very nice. Did you say you have a problem with 10'000 messages in a
mailbox?

Simon