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I would like to use the same SRs on XenServer hosts that are not able to be part of the same pool (because of not having the exact same cpu feature set, if I understand it correctly) in order to share templates, being able to (manually) start a host on another node, backing up running hosts on other hardware etc etc. The technology for SR can be any of iSCSI, NFS or CIFS, iSCSI would obviously be preferred.

Trying to add an iSCSI volume renders a "This LUN is already in use as SR iSCSI - Shared Storage on pool xxxxxx.". Adding a NFS share on one XS host, creating a template there and then checking another XS host reveals they don't agree on used space etc.

Coming from a vSphere world this is quite baffling, but if these are limitations then I will have to rethink some of the concepts for this low budget project.

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can you please confirm what NFS server are you using? – M Afifi Aug 20 '12 at 4:58
Nexentas, in v3 mode I believe. – 3molo Aug 20 '12 at 5:32

If all you are looking to share are templates, snapshots, etc. and not the VM images (VHD's), I would recommend creating an NFS/CIFS share, instead of attaching iSCSI storage. The limitation you talk about above is that only one pool can connect to an iSCSI LUN at the same time.

With NFS, you will not be able to get multipath's but for templates and snapshots this should not be necessary.

On my setup, I have an NFS share created in Nexenta, which I share on my different Xen pools which is just used to host iso's.

Also, make sure you go to the Storage tab on the NFS share and select the Rescan button.

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It's for storing running and stopped virtual machines, so I guess it's a limitation. The thing is that it works in vsphere, and it would definitely work using Xen and clvm. Perhaps I could make it happen using clvm on the XenServer dom0 and trick XenCenter into thinking it being local storage. +1 for a good answer, although not applicable. – 3molo Aug 24 '12 at 19:19
up vote 0 down vote accepted

It's simply an official limitation.

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