--On Tuesday, October 07, 2003 6:43 PM -0400 Rob Siemborski <[EMAIL PROTECTED]> wrote:r
On Tue, 7 Oct 2003, Ben Carter wrote:
and an MTA on each cluster member, because with the murder configuration, you probably have to end up with a load-balancing switch in front of murder front-end machines which in turn are in front of the
This is not the case. Simple DNS round-robining is sufficient.
How is simple DNS round-robin sufficient? More than one MUA caches the DNS lookups for its mail servers. I know that at least one version of Netscape Communicator used to. It probably still does. Also, some webmail clients do. So if a front-end is down or has not network connectivity, one gets hung MUAs.
design, backend machines would have to be clustered anyway (2-node clusters probably) to eliminate the back-end machines as SPOFs.
Well, the aggregator isn't solving the HA problem. It is doing its best to mitigate it however (via partial failure modes).
I know. The aggregator is better for us for at least one other reason: we can use our existing SCSI storage arrays. Veritas does not support clustering with SCSI (changing the host SCSI initiator IDs to be different).
And my second question is: is there something I'm missing with regard to the Veritas cluster being a much simpler configuration to troubleshoot and operate and a much stronger configuration in terms of availability?
Well its simpler unless it breaks or has poor performance.
OK. I thought so.
I'm not familiar with the Veritas cluster (we have had good experience with vxfs on our backends however). You also probably want to be sure you're not replaceing one single point of failure (a backend) with another (the cluster).
The key about the usability of the filesystem is that file locks need to be obeyed throughout the entire cluster, and mmap() needs to be efficient (and able to deal with read() and write() being called on that file at the same time).
That the locking needs to work is clear. I did not think of the mmap() vs read/write issues. Thanks.
Also, the murder does get you one performance advantage that the veritas cluster (even correctly implemented) does not: it provides a large number of read-only copies of the mailbox list that clients can use for LIST operations, and not interfere with updates of the master copy. With the size of mailbox lists on systems that are considering HA options, or moving to an aggregator configuration, this is, in fact, a serious concern to think about.
That's another good point. However, is this still an issue if one does not select the flat file format for the mailboxes file?
Has anyone implemented Cyrus IMAP with any type of clustering softwarethat you know of?
Thanks,
Ben
-Rob
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Rob Siemborski * Andrew Systems Group * Cyert Hall 207 * 412-268-7456 Research Systems Programmer * /usr/contributed Gatekeeper
Ben Carter Computing Services & System Development University of Pittsburgh [EMAIL PROTECTED] 412-624-6470
