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

Robert Edwards bob at cs.anu.edu.au
Wed Aug 13 23:36:56 GMT 2008

We have a coraid ATAoE (ATA over Ethernet) chassis here with 15 SATA
drive bays (currently populated with 8 x 1TB). Externally looks like
two Gigabit ethernet ports - can be attached to as many host machines
as you like (simultaneously). You can even use Lustre or GFS etc. to
simultaneously mount the same file-system, or you can create separate
virtual block devices on it and mount them on different machines
simultaneously. It also can do/does RAID at the block (hardware) level.

I demo'd it at CLUG about a year ago. Works flawlessly for us here.

ATAoE does not have TCP or even IP overheads (cf. iSCSI) and so, also,
has the advantage of not being susceptible to direct internet security
issues (but, as with any storage, the servers connecting to it might
be!). It's purely layer 2 connectivity only.

Heaps cheaper than fibre-channel or even firewire (Gigabit NICs cost
next to nothing these days and, if you need it, a gigabit switch is
also way cheaper than any other comparative switching device).



Bob Edwards.

steve jenkin wrote:
> steve jenkin wrote on 14/8/08 8:41 AM:
> Ummmm. Don't want to seem ignorant or lazy by answering my own question.
> [I'm still v. interested in iSCSI & eSATA, please don't let up on those]
> But one answer is Firewire - it supports multiple hosts on the same bus
> - is why it can be used for IP (as well as things like fibrechannel &
> infiniband - which are switchable, but out of $$ reach).
> This isn't exactly what I had in mind, but points there.
> <http://www.macosxhints.com/article.php?story=20080717051811427>
> The hint was in wikipedia - 1394a supports multiple hosts.
> <http://en.wikipedia.org/wiki/1394a>>
>> 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.
>> 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?
>> A good fallback position for me is a NSLU with USB attached disk.
>> But that introduces yet another point of failure...
>> cheers
>> steve

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