Ok, so, I might want to put the 3rd backend on controller 1, and then a
4th backend on controller 2.. and so on like this
Controller 1
Backend 1
Backend 3
Backend 5
..
Controller 2
Backend 2
Backend 4
Backend 6
..
-Tony
---------------------------
Manager, IT Operations
Format Dynamics, Inc.
303-573-1800x27
[EMAIL PROTECTED]
http://www.formatdynamics.com
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Emmanuel Cecchet
Sent: Monday, June 16, 2008 12:26 PM
To: Sequoia general mailing list
Subject: Re: [Sequoia] help understanding multiple controllers with disk
spaceusage
Hi Tony,
> Kind of..lets see if I got this..so with my first setup, which was
just
> 1 controller, that controller talks to both my db backends (i.e. I had
2
> backends in the virtual database config file), but now with the setup
of
> an additional controller, I should move the backend config for the 2nd
> database server to the 2nd controller? So each controller is only
> talking to 1 backend?
>
Yes.
> If so, what happens when I add a 3rd database server/backend? In what
> controller would that get configured? If I add it to just one
> controller, and that controller goes down, then I lose consistency on
> that backend through the 2nd controller (which doesn't have it
> configured), if it was configured on both I'd have multiple writes and
> inconcsistency again, as you mentioned. Would I need a third
controller
> then?
>
If you add a 3rd database, you can attach it to one of the controllers
(but as you mentioned when you lose that controller you will lose both
databases that are attached to it) or use an additional controller. The
tradeoff is that additional controllers slowdown the group communication
and add some more management but you will loose less backends in case of
a failure.
In your case I think I would stick with 2 controllers.
Hope this helps,
Emmanuel
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of
> [EMAIL PROTECTED]
> Sent: Wednesday, June 11, 2008 11:42 AM
> To: Sequoia general mailing list
> Subject: Re: [Sequoia] help understanding multiple controllers with
disk
> space usage
>
> Hi Tony,
>
>
>> >From reading the docs, backends cannot be shared between
controllers,
>>
> so
>
>> does that mean that a 2nd controller added (in a RAIDb1 scenario)
>> reduces disk space on each database server by half?? E.g. if I have 2
>>
> db
>
>> servers, each with 500GB of space and one controller (w/2 backends),
>>
> the
>
>> database on each server can grow to 500GB, but with 2 controllers,
>> there's 2 copies of the database on each server, so it could only go
>>
> up
>
>> to 250GB then? And then if 3 controllers, the space would be 1/3 of
>> 500GB (166.67GB).
>> Am I understanding this correctly?
>>
>
> No. The only thing it means is that each db server can only be
accessed
> by
> a single controller.
> If you have 1 controller, your 2 db servers must be attached to that
> controller.
> If you have 2 controllers, each controller is connected to 1 db
server.
> If you have 3 controllers, 1 controller will have no database server,
> and
> the 2 others will have one each.
>
> As each controller sends the write queries to all its attached
backend,
> a
> backend attached to multiple controllers would receive the same query
> multiple times and be inconsistent.
>
> Does that make sense?
> Emmanuel
>
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>
--
Emmanuel Cecchet
FTO @ Frog Thinker
Open Source Development & Consulting
--
Web: http://www.frogthinker.org
email: [EMAIL PROTECTED]
Skype: emmanuel_cecchet
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