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
_______________________________________________
Sequoia mailing list
[email protected]
https://forge.continuent.org/mailman/listinfo/sequoia
_______________________________________________
Sequoia mailing list
[email protected]
https://forge.continuent.org/mailman/listinfo/sequoia
--
Emmanuel Cecchet
FTO @ Frog Thinker
Open Source Development & Consulting
--
Web: http://www.frogthinker.org
email: [EMAIL PROTECTED]
Skype: emmanuel_cecchet
_______________________________________________
Sequoia mailing list
[email protected]
https://forge.continuent.org/mailman/listinfo/sequoia
