Re: [Xen-users] Advice on redundant SAN/NAS storage for Xen

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Sun, May 31, 2009 at 12:49 PM, Rudi Ahlers <rudiahlers@xxxxxxxxx> wrote:
> And my question, on this same topic, would be, what is wrong with
> using 2 standard servers (i.e. not a dedicated, expensive NAS device)
> with 2 or 4 HDD's each, setup with something like DRBD / RedHat
> Cluster Suite to offer one single redundant NAS / SAN server?

Nothing's wrong, if you understand how it works, plus its consequences.
For example, there's fencing issues on RHCS, which has caused
frustration for some people. Plus it requires that you have a shared
storage, which (from the example you give) you don't.

Can you emulate the shared storage using DRBD? Sure. But it introduces
another layer of complexity.  Plus you need synchronous
primary-primary mode which introduced additional complexity,
performance penalty, and (taken from drbd site) "These systems are
very sensitive to failures of the replication network. Currently we
cannot generally recommend this for production use"

If you understand the requirements and its consequences, and decided
that you can accept it, then it's probably good for you.

IMHO it's not worthed. If I had that hardware I simply use them
directly as dom0, with scheduled replication among each node. It does
not provide automatic failover, nor support for live migration, but it
greatly simplifies system setup and gives maximum I/O troughput.

> Or, even
> using something like http://www.openfiler.com/ or
> http://www.freenas.org/ ?

Their greatest feature is that they can convert an ordinary x86 server
into iscsi SAN/NAS.
They can't use the example setup you give and turn it into an
enterprise SAN replacement.

If your main goal is domU migration, and you can live with the SAN/NAS
being the single point of failure, then those are good choices.
Personally I'd use opensolaris for their excellent (and supported)
zvol feature. If you have enough budget you might also want to look at
Sun's Unified Storage.

-- 
Fajar

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