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I have two physical servers that I'd like to setup for virtualization. I'd like to set them up in such a way so that the following goals are met:

  1. Allows live migration of guest OSes from one server to another, if I have to take one of the physical servers down for maintenance.
  2. If the hardware of one of the servers dies, I can do a cold migration of its guest OSes to the other server (i.e. all data is sync at all times between the two physical servers).
  3. Underlying storage for guest OSes can be efficiently snapshotted once every hour or once every day (e.g. using ZFS. I'm ruling out LVM, since taking multiple snapshots in LVM is inefficient).

Since OpenSolaris provides ZFS, I'm thinking using OpenSolaris/xVM as a dom0 would be a good fit. However, my understanding is that in order to allow live migration, you need to have another server (SAN) for shared storage, and I'd rather not add another server for cost reasons.

If it wasn't for the fact that ZFS isn't available for Linux (except through FUSE, which I'd rather avoid), I know I could set something like this up for DRBD. Could I do something similar to that with OpenSolaris? I've read about AVS, but I'm not sure if live migration can be made to work with that. Or if you have any other suggestions that use a different OS, I'm open to that as well.

Thanks!

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I would be interested in seeing you add an answer if you make a decision on what you decide to do and what rational guided your decision. I have been wanting to try Xen out but didn't realize the live migration required shared storage. I guess that means the hardware being used for shared storage is kind of the weak link? –  AaronLS Aug 23 '10 at 19:17
    
Will do. Yes, shared storage would be the weak link, unless you have redundancy in that as well (i.e. mirror all data between two iSCSI servers/SANs). Alternatively, you could use DRBD on the two Xen dom0s and replicate storage that way if you run Linux dom0s. I've set this up before and live migration works fine on top of DRBD - no SANs necessary. Of course, you don't get ZFS that way. :) –  Alex Aug 25 '10 at 3:38
    
In light of the answer that was recently added to this question, I might just end up foregoing the live migration functionality for now, and just stick with cold migration. To do a cold migration, I would just power down the guests on the first machine, execute "zfs send" and "zfs receive" to replicate storage volumes between the two machines, and then bring up the guests on the second machine. –  Alex Aug 31 '10 at 15:25
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What you are asking for isn't possible. The closest you could get would be to use iSCSI on each host for domU storage, which would allow you to do a live migration to the other host, but you will not be able to power the host down as it still will hold the iSCSI volume.

To be able to allow live migration between two hosts, you need a third. You don't have to use a SAN, you can just use a third OpenSolaris to host the iSCSI volumes.

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