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I'm planning a redundant set-up for VMware. Two locations (about 8-12km distance) are to be connected with dark fibre for SAN connectivity. I am looking for a FC-SAN product that allows transparent failover for VMware Fault-Tolerance. This means, that if one SAN is offline the other SAN will promote the LUNs automatically .
Neither NetApp nor EMC does seem to provide this featue...

Any hint?

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4 Answers

up vote 3 down vote

What is transparent failover and do you really want it? Geo fault-tolerance is pretty difficult to do with any form of performance. Fault tolerance has already got a number of performance/scalability limitations, 1 vCPU, lock stepping etc, you need the same shared storage etc.

You do not in any circumstance want automatic DR failover, you want a big red button to push to execute it, coordinated in a formal decision making process. Small glitch and you are looking at a complex fail back process.

Both Netapp and EMC offer replication and storage failover in conjunction with VMware Site Recovery Manager. Netapp Snapmirror Sync or EMC SRDF but make sure you test performance of your apps etc before you enable this. If your sites are close enough together and you'd don't need to failover hosts etc you could look in to Netapp Metro Cluster with SyncMirror.

One way to do this would be if VMware added storage FT, writing a VMDK on two datastores.

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Thanks for your input. I'm aware of the VMware limitations. However, I do not want a big red button; I want a fully automated failover system with manual recovery. – CyberOptic Mar 22 '11 at 10:50
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I doubt you do :) But Netapp Metro Cluster could be an option if you really do. – HampusLi Mar 22 '11 at 11:30
For VMware you would use it's Site Recovery Manager product which needs array integration for the LUN magic. I think one should probably point out that there should be no fault tolerant metro/geo storage available that should automagically promote the shadow LUNs from read-only to read/write and break the replication as this may be not nice to your application(s). All storage replication schemes/approaches work that way. – pfo Mar 22 '11 at 15:33
pfo: AFAIK does the SRM not act automatically, meaning that the "big red button" has to be pushed? – CyberOptic Mar 22 '11 at 15:37
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up vote 1 down vote

HP EVA can do this with the right software. Specifically, you're looking for:

  • A pair of EVA6400/8400 disk arrays
  • Command View EVA
  • Continuous Access EVA
  • Cluster Extension Software

The second two bullet points are the meat of it. The last bullet point will be your second biggest cost after hardware.

There are some significant limitations to this, though. The replication between the two arrays has to be in Synchronous mode, so writes will only be considered committed if both arrays report it committed. 8-12km does introduce latency, and it could be very significant latency if your applications are sensitive to storage latency.

That said, it does what you're looking for. Automatic failover between disparate storage arrays without human intervention.

Unfortunately, the above is not VMWare-certified. If that matters to you, it's not doable.

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Sounds like what I wanted, but it has to be certified... Thought the EVAs are certified already? – CyberOptic Mar 22 '11 at 13:32
@cyberoptic they are, but the config is not. Vmware is picky that way. – sysadmin1138♦ Mar 22 '11 at 14:34
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What type of VM functionality are you looking at deploying, I do multi-site failover but I have the luxury of effectively static web and app VMs so just duplicate them around the place and use Cisco GSSs to load-balance over sites. Where I have problems is with my DBs which aren't VM'ed and are out of synchronous range so I have to use DataGuard/GoldenGate to async them. If your VMs aren't 'static/stateless' then you do need your LUNs replicated, have a look at HP and/or 3Par, they can do this in conjunction with VMWare's Site Recovery Manager but to be honest I'm surprised NetApp (whose boxes I despise btw) can't do what you want.

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Thanks for your information. I want to utilize VMware FT. The guests and its applications/services are own-developments with an properitary TCP protocol stack. – CyberOptic Mar 22 '11 at 13:31
That's going to be one seriously busy stetched FT vlan! – Chopper3 Mar 22 '11 at 21:31
not that busy. i got about 3mbit max for 2x4 VMs w/ FT. and we've got a whole dark fibre to multiplex. – CyberOptic Mar 23 '11 at 7:52
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up vote 0 down vote accepted

FYI: I looked around and found DataCore SANsymphony that seems to provide the automatic failover functions. I'll have it deployed in our test environment.

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