High availability ... again

[Michael Loftis]

--On Wednesday, June 23, 2004 11:48 -0700 Kevin Baker 
<kbaker at missionvi.com> wrote:

> David,
>
> This is exactly what I had in mind. Could you maybe give a
> quick overview of how you have the replication and
> failover setup; specifically "application level
> replication vs block"

application lvel means exactly that.  The actual program/server software 
involved does it's own replication.  Like Oracle RAC or MySQL replication. 
block level means soemthing at the disk I/O layer does it all, without the 
app's knowledge.

>
> While the idea of a standby server that uses block level
> replication seems very great, if possible I'd like to have
> the reliability while still being able to use both
> machines.
>
> Is it something like this:
> - Server A
>   - active accounts 1-100
>   - replicate accounts 101-200 from Server B
> - Server B
>   - active accounts 101-200
>   - replicate accounts 1-100 from Server A
>
> If B goes down, A takes over the accounts it had
> replicated from B.
>
>
> Thanks,
>
>
>
>
>
>
>> 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.
>> ---
>> Cyrus Home Page: http://asg.web.cmu.edu/cyrus
>> Cyrus Wiki/FAQ: http://cyruswiki.andrew.cmu.edu
>> List Archives/Info:
>> http://asg.web.cmu.edu/cyrus/mailing-list.html
>>
>
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>



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labeled `occupant.'"
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