VMFS Storage - LUN mirroring ("RAID-1")

[fejf]

Hi,

I want to implement a failsafe storage environment with 2 SANs. The normal windows and linux way would be to create 1 LUN on each SAN and use a software RAID-1 on the two LUNs. I know that this isn't possible with VMFS. As the used SANs can not provide the mirroring I'm searching for other possibilities. My current ideas include:

- A linux/bsd/openfiler box which creates a RAID-1 over the two LUNs and presents the mirrored LUN as software iSCSI target (problem is that this may be a bottleneck and it needs to be clustered -> difficult to setup/make this failsafe)

- Use SRM/VCB/... to make daily backups of the VMs from one LUN to another (but that can lead to massive dataloss of 24h...)

- Buy new SANs which provide the "virtual LUN" feature (aka ESX-Server only sees one (virtual) LUN but actually the data gets written (mirrored) on two SANs)

Are there other (and better ways of achieving the "RAID-1"-goal? Can anyone tell me which SANs provide a "virtual LUN" feature and are certified for VMware ESX?

--

There are 10 types of people. Those who understand binary and the rest. And those who understand gray-code.

[williamarrata]

You may wanna review this document for your SAN questions.

Hope that helped.

[fejf]

What exactly do you mean? I've read parts of this paper before and reread parts

of it again but I can't find anything related to my questions

--

There are 10 types of people. Those who understand binary and the rest. And those who understand gray-code.

[mgoheen]

I'm in the exact same position -- we use software mirroring on all our various clients (Linux, Windows, Solaris), but now that we have started looking at ESX, we find we are stuck (or have to buy something).

The "answer" given above only documents what the original question asks -- e.g. it verifies that there isn't a way to do what he wants.

The basic question is, "Is there a way to do software mirroring on to two channels of a SAN for VMFS?"

As far as I can tell, the answer is no.

[Nick_F]

Not heard of this method before, I guess it's quite a neat solution but don't you hit performance issues using software RAID? Also presumably it doesn't scale well (you wouldn't want to run a large DB server on a RAID-1). Presumably the SANs are co-located so I can't see you're getting much redundancy benefit (SANs themselves are usually very reliable with a lot of redundancy built in). I guess the only real solution is to use SAN replication software (which would depend on your SAN model and whether you need synchronous or asynchronous replication).

[mreferre]

This is a question that pops up every day.

The short answer is that you can (actually could) do this: http://it20.info/files/3/documentation/entry2.aspx

This is a project I have been working on some 2-3 years ago and we have implemented just that.

Notice: that was the ESX 2.x time frame and the architecture at that time (VMX files on the host / DSK files on the SAN) made this easier. The current VI3 architecture (both VMX and VMDK files on the SAN) make this trickier (i.e. there is no easy way to mirror the VMX file in this context).

A work-around that has been evaluated lately was to use a NetApp (or NetApp-like) solution that allowed to put the VM directory (i.e. all files including the VMX and except the VMDK files) on a shared fully redundant and transparently replicated NFS/iSCSI storage.... and put the VMDK on the SAN to be replicated through storage server hardware algorithms.

Massimo.

[mgoheen]

Well, our "SAN" is really just a disk farm (about 100 or so disks hooked up to Fibre switches). Allocation is "disk at a time" (but really two at a time, since everyone mirrors). We don't run any virtualized database servers. I'm not certain it doesn't scale -- each hardware system has dual channel Fibre controllers (or two controllers) and there is plenty of backplane bandwidth to support two channels (the bottleneck has always been in the Fibre channel itself -- although now with 8Gbit Fibre things are perhaps catching up).

At any rate, yes, you CAN do the mirroring in the virtual host, but that is much more complicated.

We aren't a big site (only about 30 or so servers). I'm certain I'd have to approach this much differently if we were larger...