2 LUNs mirrored in one datastore?

[Neil_C]

I have a question which I think I know the answer but I would be interested in some verification.

We have 2 computer rooms, with a SAN storage system in each room. Then we have, for example, one ESX server which is given a LUN from each SAN. What I would like to do is add both these LUNs to one datastore but in a mirrored configuration so the end effect would be that we could lose one SAN storage system without any interruption. This is the kind of configuration we have on our Unix systems but I don't think this is possible in VMware but I cannot find any information on implementing this so I guess it is not supported or possible?

If this isn't possible how do others provide redundancy in case of a SAN system failure/outage?

Thanks,

Neil.

[Texiwill]

Hello,

VMware ESX can not provide this functionality but VMware SRM (when it comes out) should provide what you want. At the moment the only real option is to use SAN based tools to do the same. Depending on the SAN product you want something like HPs Continuous Access which will mirror continuously between two LUNs. Mirroring in the hardware is MUCH MUCH better. I would start investigating your SAN options.

If your SAN does not support this, then you need an intermediary that does. One option is to setup an iSCSI server running Linux who has access to the LUNs. Using Linux Software RAID you could create a volume which you could then present to ESX using the iSCSI Enterprise Target code. I have used software RAID before but not quite in this fashion. It should work. Contact me via PM if you wish to pursue this.

Best regards,

Edward L. Haletky

VMware Communities User Moderator

====

Author of the book 'VMWare ESX Server in the Enterprise: Planning and Securing Virtualization Servers', Copyright 2008 Pearson Education. CIO Virtualization Blog: http://www.cio.com/blog/index/topic/168354

As well as the Virtualization Wiki at http://www.astroarch.com/wiki/index.php/Virtualization

[kjb007]

SRM would be able to handle two arrays and manage vm's on the LUNs, but it will not do the replication. You would still need to have the data available in both places with array-based replication, if I'm not mistaken. As you said, hardware replication is definitely the best way to go.

-KjB

[Neil_C]

Thanks both of you for the replies.

We have Hitachi SANs and we can do data replication between SANs but I was hoping for a way to provide redundancy of SAN storage without the outage needed to pick up storage from the other SAN.

I've seen mention of providing virtual machines with two virtual disks from the different datastores (one datastore on each SAN) and mirroring within the virtual machine. Does anyone have any experience with this? I guess it's possible but ESX cope with the loss of one SAN and will it reintroduce the datastore once the SAN comes back?

Thanks,

Neil

[aguacero]

In addition to the san replication, you may want to look at possibly adding a SAN "Gateway" which would virtualize your two SANs into one virtual huge SAN pool. This way you can redirect your traffic thru the gateway and let the gateway be your "HA" point.

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[kjb007]

Either way, you have to "break" the mirror somewhere along the way. With replication in place, your data is available in the 2nd location, but as for any other mirror, it should be one-way, and in order to use the secondary dataset, you have to break the mirror, so that it is writeable. Once the mirror is broken, the data is ready for use, and the vm's data should be available on the LUNs that were replicated. All you would need to do at that point is rescan your HBA's, making sure you allow snapshot LUNs, and then register the vmx files that you see in the datastore. That is the part that SRM automates for you. You have this information already set, and once you "push the button", SRM will do all those tasks for you.

-KjB