[clug] Dual-ported disks - or accessing disks from 2 systems

Adam Thomas adam.lloyd at gmail.com
Wed Aug 13 23:42:59 GMT 2008

On Thu, Aug 14, 2008 at 08:41:01AM +1000, steve jenkin wrote:
> I'd like to be able to access a disk from two different systems,
> /cheaply/.  Anyone done this or seen it done?
> *Not* simultaneously update the same filesystem, but just to fail-over.

Depending on the use case DRBD might be an option. If all you want is
to have two machines able to hot fail over and have the disk up to
date then it might work. It does mean buying two disks though.

> Last time I did this was SUN + fibrechannel + disk array + Veritas.
> Out of the ballpark for this application :-)
> I have a hack that should work, though the manufacturer doesn't
> guarantee it. I've a Lantech Nexstar-3 with multiple-ports (USB,
> firewire, ...) *all* are active at once. I've confirmed connecting
> simultaneously won't damage the electronics. But the semantics of which
> interface gets priority is unclear & this mode not officially supported.
> What I'd *really* like is something based around SATA/e-SATA - do SATA
> switches exist? Ie. connect two HBA's to one device.
> Or if anyone can recommend a good/cheap iSCSI setup, that'd be interesting.
> Can anyone tell me how much CPU overhead & network bandwidth iSCSI burns?

Have you thought about AoE? It is similar to iSCSI but with less
features and much less overhead. For a setup where you are thinking
about sharing an ieee1394 bus I doubt the lack of routabiity would be
a problem.

> A good fallback position for me is a NSLU with USB attached disk.
> But that introduces yet another point of failure...

Some one else on list has suggested using AoE on an NSLU before and
that sounds like it might work out quite well for you. It's cheap,
doesn't add any more SPOF than an iSCSI controller would and is low 
CPU and network overhead means it should be fast enough.


> cheers
> steve
> -- 
> Steve Jenkin, Info Tech, Systems and Design Specialist.
> 0412 786 915 (+61 412 786 915)
> PO Box 48, Kippax ACT 2615, AUSTRALIA
> sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin
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