Hello,
I started to build HA cluster with 3 servers running Xen Server and SAN for storage repository. I haven't made such installation so far and I am wondering how to organize the SAN.
First of all I read a lot of controversial opinions concerning the LUNs. Some people claim there should be 1 VM per LUN while other say you can put many VMs on a single LUN.
What is the right solution. I see advantage on 1 VM per LUN if I want to make LUN snapshots and to copy those snapshots to another SAN (which I have).
The other question is should the LUNs be thin or thick provisioned. I understand the advantages of the thin provisioned LUNs, but I read somewhere performance is affected with them. What do you think?
And the last thing is what RAID to be configured on the SAN? The SAN is 12 SAS HDD and definitely there will be mirroring - RAID 1. But should I make RAID 0 between the disks?
Thank you in advance

I don’t quite understand what you mean by “VM per LUN”. VMs can share storage, but each requires its own root disk. Can you elaborate?

You may have a tiny performance penalty each time a new block is allocated on a thin LUN, but my guess is that you would not notice. Thin provisioning is good for space efficiency, but you risk not having enough space at some time. If your VMs rarely use all their allocated space, use thin provisioning. If the VMs belong to customers, use both thin and thick, and charge more for thick.

Regarding striping, Veritas says “Striping is useful if you need large amounts of data that is written to or read from physical disks, and consistent performance is important.” Does that describe your application?

Thank you, berndbausch.
My question is should I put each VM virtual disk on a LUN specially created for it or I can create a LUN for example 5 TB and to put 5 Virtual machines disks 1 TB on it.

My experience is with OpenStack mainly. There, each VM either gets a file on its hypervisor host as root disk, or a so-called volume, which usually corresponds to a LUN.

I don’t see an advantage sharing LUNs, but it would be hard to manage, snapshots included.

Here is a link where they say you can put 10 VMs on single LUN. I don't know what to do.
https://loopbackconnector.com/2012/0...ioning-primer/

The article doesn’t explain what’s the advantage putting several VMs onto one LUN, and what’s the disadvantage to have one LUN for one VM. Perhaps it’s specific to VMware six years ago?

I suggest looking for more recent resources, perhaps from VMware directly.

I have not worked with Xen. But when I used to manage ESXi cluster, always did 1VM/LUN. Reason for that is in hardware failover situation, we needed some VMs on certain hosts and others on different (due to resource requirements). This would have been difficult if multiple VMs are on same LUN. So, not sure if you have this kind of requirements now, but perhaps plan for future?

This may depened on your environment. For example, my ESXi cluster was for Exchange environment for a university (several thousand users), so all of the disks were thick provisioned.
Currently managing Hyper-V cluster (for under 100 users) and here all VMs are thin provisioned, and users do not report any performance issue. Some of the users jobs are heavy in IO.

Don't understand this question... For 12 drives, I would personally do RAID50 (create two RAID5 sets with 6-drives, then RAID0 of two RAID5 sets).

Hope this helps?