[CentOS] iSCSI Question

Sat Nov 17 23:23:08 UTC 2012
Digimer <lists at alteeve.ca>

On 11/17/2012 06:08 PM, Steven Crothers wrote:
> On Sat, Nov 17, 2012 at 12:34 AM, Ian Pilcher <arequipeno at gmail.com> wrote:
>> There's a reason that those proprietary vendors are able to charge big
>> $$$ for this functionality.
> That's the truth... I was hoping they were based off some open source
> implementation of iSCSI somewhere.
> I mean I could probably dedicate a single machine to run iSCSI and just
> schedule downtime, but that's something I wanted to avoid.

You could take two nodes, setup DRBD to replicate the data
(synchronously), manage a floating/virtual IP in pacemaker or rgmanager
and export the DRBD storage as an iSCSI LUN using tgtd. Then you can
migrate to the backup node, take down the primary node for maintenance
and restore with minimal/no downtime. Run this over mode=1 bonding with
each leg on two different switches and you get network HA as well.

I've done this to provide storage to a cluster of VMs and I could even
fail the primary node and the backup would take over without losing any
of my VMs.

I didn't speak up earlier because of all the other features you asked
for, but this will at least give you your HA requirements.

> I've been looking at something like Open-E, but it's active/passive with
> what is essentially a DRBD link between them. Again, not ideal. Speaking of
> which, why do people rely so much on DRBD for LAN deployments lately?
> Everyone always seems to cheap out and setup
> DRBD/Pacemaker/Heartbeat/*insert some HA software here* instead of using
> proper clustered file systems. DRBD to me has always screamed WAN
> replication. Maybe I just don't put enough value in it, who knows.
> Anyway, back to my hunt for a way to implement my Ceph cluster on Windows
> 2008.

Clustered filesystems like GFS2 and OCFS2 come at a non-trivial
performance hit. It's usually a case of avoiding them when possible.
Using DRBD is not "cheaping out". I prefer it to fancy SANs as it's more
HA than a SAN.

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