Re: NAS

On Thu, 17 Sep 2009, Marco Fortina wrote:

> A customer of our company would like to create a 2 nodes cluster
> connected to an external NAS storage. I would like to know if PostgreSQL
> supports its datafiles on this kind of storage and if this solution is
> certified.

It's possible to setup this configuration with PostgreSQL, but all of the
failover logic needs to be implemented with another program that does
things like making sure only one copy of the database server can be active
at a time.  There are a couple of products that aim to handle this
situation around.  The FAQ for EnterpriseDB, who sells a commercial and
supported version of PostgreSQL, talks about a couple of them in a helpful
way:

http://www.enterprisedb.com/products/allfaq.do

I believe (and the FAQ suggests) they've got some setups like this among
their customers already.

Any of the projects they mention, Linux-HA, Red Hat Cluster, or Veritas
Cluster, *could* be made to handle this goal, but it's going to require
some customization to make that work for your customer.  Should still be
much less expensive when it's all said and done than similar offerings
from the better known database vendors up-front, particularly when you
consider the annual license fees of some of them for clustered solutions.

Open-source projects such at PostgreSQL don't "certify" things as working;
that's the sort of job better a company selling products.  There are
subtle hardware issues you need to be aware of with NAS to get both
reliability and good performance, and as I already suggested lots of work
to get the software right too.

EnterpriseDB might have a certified production suggestion available, and
you can find plenty of other companies who do this sort of work in the
directory http://www.postgresql.org/support/professional_support ; I'd
suggest you peruse that.  Other companies on that list who I know do lots
of custom replication consulting work include 2nd Quadrant, Command
Prompt, and End Point.  It would be pretty expensive to develop something
in-house for this approach starting from scratch.  I'd guess some number
of months of full-time work for someone who was new to PostgreSQL and/or
replication before they got it right. In my role as full-time pessimist, I
would also suggest you definitely don't want to rely on anybody's first
attempt at setting up replication, it's complicated and way to easy to
screw it up in a way you won't notice until your data has already been
eaten.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD