High availability ... again

[David Carter]

On Tue, 22 Jun 2004, Etienne Goyer wrote:

> Does somebody on the list use this solution or a similar one and could 
> comment and the practicality of it ?  Perhap M. Carter (if you read the 
> list) could give us a status update for his particuliar project ?

There's really not a whole lot to say.

We've been using the code on our main 32k user mail system since about 
this time last year for data migration, fast incremental backup to a tape 
spooling system, and rolling replication for live updates. We also used 
the replication system to migrate from a UW based system to Cyrus.

We have 16 small Linux servers running as 8 pairs. All the systems are 
live Cyrus servers, half the accounts on each system are replica versions.

One of the 16 had a hardware fault a couple of weeks back and noone has 
moaned at me after we switched to the replica which is always a good sign.

>From my perspective the advantage of application level replication over 
block level replication like DRDB is flexibility. Read/write access to 
both master and replica systems can be useful: we maintain databases
of MD5 checksums for all the messages and cache entries on each server.
Its also rather cute to run PINE against both master and replica version 
of a given mailbox and watch the replica play follow my leader :).

-- 
David Carter                             Email: David.Carter at ucs.cam.ac.uk
University Computing Service,            Phone: (01223) 334502
New Museums Site, Pembroke Street,       Fax:   (01223) 334679
Cambridge UK. CB2 3QH.
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