Re: Er.... for Sendmail users......enough

Christopher E. Brown wrote:
> Pairs of Cyrus servers acting as hot and standby for a shared SCSI or
> iSCSI target. Each server pair handles a subset of the users. Proxy
> redirectors send the user session to the correct back end server. If a
> server fails that subset of users is offline till the standby takes over.
> OR
> NetApp/other based NFS shares, with a hashed maildir directory tree. The
> tree can be on one netapp, or spread across multiple units for performance
> reasons (already assuming netapp == netapp cluster with FC-AL takeover).
> Since true maildir is lockless and multi-access/NFS safe you can
> have 10 - 20 Courier servers, all mounting the tree, and any system is
> able to handle any account. No proxy-redirection required. Same applies
> on the delivery side, any SMTP host can deliver to any account.

This is an excellent point and something to consider depending on your
availability and performance requirements. From one perspective the
lockless nature of maildir/courier really makes clustering simple, but I
doubt it will be as fast at some operations (not even a netapp can
open/parse/close 4700 files in .050 seconds), and you still depend on a
single file system.

Cyrus has murder which an IMAP/POP3 aggregator. This allows you to have
a cluster of servers and split up the mailboxes between them, but that
doesn't buy you any fault tolerance. To solve that problem, the new
version of Cyrus now supports replication so you can have your mail
sync'd to a hot standby in (near) realtime, but this solution is much
more complex than the courier setup mentioned above.

Some people have deployed two instances of cyrus on two servers, and
setup half the mailboxes on one server as primary, and the other half on
the second server as primary. They then have the second instance on
server A act as secondary to the primary instance on server B and vise
versa. This is complex, but does buy you complete redundancy without
buying a netapp.

Given the pros and cons, I would probably mock up both solutions in my
lab before making the call. On one hand cyrus is very efficient and
very quick, but has a bit more complexity when doing replication. On
the other hand courier looks very simple to cluster, but probably would
not perform as well when fetching headers or searching.

I also wonder about how well sendmail/courier would work togther, I'm
not willing to give up milter, and as far as I can tell the only way to
get sendmail to write email to a courier maildir box is with procmail
which I'm not a real fan of.

Perhaps I'll play with this in the lab in the next few weeks. I have
been wanting to do my own benchmarking of a few different mail solutions
anyway.

Thanks,
schu

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Received on Thu Aug 31 05:07:34 2006