Daniel Feenberg writes:
 > 
 > Wouldn't rsync do a better job with an MTA using "maildir" format for
 > message delivery? After all, given two alternative /var/mail/userid files
 > with different "last write" dates, what is rsync to do?

rsync is rife with options. You could tell it not to overwrite files
on the target that had a newer mod time if that's really what you want.

It sounds like you're looking at having users access both stores at
the same time, or having mail be delivered on both systems at the same
time - neither are going to work very well! There's an implication here
that any rsync solution should be strictly active-passive - the backup
server should not be active until it is explicitly enabled. I did not
mean to imply that rsync was somehow going to give you any consistency
when updates happen at both ends! It's not replication, its a hack that
could meet the need and be a whole lot cheaper.

For concerns about a single system going down at one site, external HW
RAID with hot standby and/or full-on HA solutions are going to work much,
much better. Having said that, I have cobbled together rsync-based
solutions for budget-conscious customers looking to meet the 80/20 rule.
Sun & Veritas licensing can be, uhm, expensive...

But what if the concern is that you have backhoe induced fadeout of
your network or power at a central site? Is it acceptable to switch to
a server with X hour old copies of the mailstore? How will you get the
4-500 users to use the new mailstore? Sometimes the answers to these
questions indicate you can go with this sort of rsync-based approach,
and sometimes they don't.

--Steve.

PS - Tony, thanks for the info about NetApp! Hadn't thought of them.



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