[ale] AoE and Cluster-Aware Raid

[Ed Cashin]

On Mon, Oct 13, 2008 at 10:37 AM, Jeff Hubbs <hbbs at comcast.net> wrote:
> I'm trying to acquire some mojo on ATE over Ethernet and specifically
> having multiple initiators (think "clients") make RAID volumes out of
> multiple separate targets (think "servers").  Googling turned up
> mentions of having cluster-aware kernel RAID "real soon now" in the
> 2006-ish timeframe.
>
> Anyone knows where this stands now?

[Disclaimer: I work for Coraid, who sells AoE target hardware.]

If you could point me at any "RSN" announcements for
cluster ability in Linux Software RAID, I'd be interested
to check them out.

When you are talking about a many-to-many relationship
between the AoE initiators and targets, the assumptions
that md makes don't hold, because md assumes it's in
exclusive control of the components in the arrays it maintains.

There are some folks using the mirroring feature in LVM,
I believe, even though it's kind of scary to me, because it
seems to be the "road less traveled."  You need the cluster
features of CLVM to have all the initiators share the same
view of the mirrored storage.  A mirrored CLVM logical volume
provides redundancy between AoE targets.

Coraid put mirroring in the VS appliance largely to address
the need for clusters that needed redundancy between AoE
targets.

On the other hand ...

You can always go low-tech and use a file server pair.
For example, you set up two NFS servers that use md
and heartbeat.  The NFS servers are active/passive and
can failover, and the active one runs md over the multiple
AoE targets.  Now the many users of the storage are NFS
clients instead of AoE initiators.

-- 
  Ed Cashin <ecashin at noserose.net>