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I'm about to deploy XenServer on a DELL R900 and haven't finalized on the Storage yet. Would typically be running like 40 VMs on the server with requires about 2TB of storage.

What should I choose Local Attached Storage, NAS, SAN? Need to build a soultion that gives a better performance, scale-up and backup options.

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    What is your budget? Do you have any NAS or SAN solution in place already?
    – Christopher
    Commented Oct 7, 2010 at 16:22

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If you have just a single R900 server to dedicate to this project then there is no reason not to use local storage - it's going to be the cheapest and the fastest. I will not turn this discussion into a disscusion about if this is something you should do or not :-) 40 VM's running on a single server may or may not have the preformance/redundency that you require - that is another topic.

SAN storage is required when you have multiple servers dedicated to hosting your VM environment. The shared nature of the SAN allows each server to have access to the VM files. This allows things such as vMotion (or Live Migration).

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    Great point Richard, I'd add that he should go for 15/10k SAS disks if he cares about performance too.
    – Chopper3
    Commented Oct 7, 2010 at 17:01
  • My two bits: a 10:1 virtual-to-physical host consolidation ratio is pretty standard for your typical mix of Windows and *NIX variants running common line of business applications/platforms like Exchange, SQL, SharePoint, etc. 40 sounds a bit aggressive in my opinion unless these are primarily *NIX VMs under light load.
    – gravyface
    Commented Oct 7, 2010 at 19:13
  • That's changed in recent times, as newer hardware is kitted up from the get-go to support virtualisation and can take higher overall RAM capacity. We're running a ratio of 30:1 in production, and one isolated environment that's running mostly test scenarios is at 56:1 right now. In both cases we're hitting RAM limits first.
    – Chris Thorpe
    Commented Oct 7, 2010 at 19:16
  • Guess it depends on the vendor: IBM was still saying 10:1 as of yesterday.
    – gravyface
    Commented Oct 7, 2010 at 19:27
  • Yes, bu those aren ormally general guidelines. There are a LOT of scenarios where the VM's are a low load scenario or just very small and break out from the averages.
    – TomTom
    Commented Oct 21, 2010 at 15:08
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The answer depends entirely on what you need your storage to do.

Will you ever connect more than one XenServer to your storage? If so, local is not a good option. What is your price point? SAN/NAS are more expensive than local, and if you have a small budget you may be able to afford the disks only as a dumb DAS or internal storage. Do you need "SAN" features, such as thin provisioning, deduplication, snapshot copies? Are you willing to pay extra for them?

Additionally if you go for shared storage (NAS or SAN) you need to decide on which protocol you are going to use to access the storage. NFS, iSCSI, FCP, etc. There are advantages and disadvantages to running NFS vs iSCSI in XenServer. It really depends on what your needs are.

Also remember that XenServer's local storage is limited to LVM over iSCSI Storage Repository types. This is a thick provisioned SR, so you are going to be forced to use thick provisioning for your storage. I am nearly positive that in XenServer there is no way to do thin provisioning without using NFS (which requires shared storage such as a NAS or SAN).

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