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I want to setup a virtual network with 2 hosts and 4 VMs. I will have an equalogic SAN.

I want to share a LUN between two VMs, one on each Host.

The objective of the operation is to use ARR for IIS with sharing configuration.

To response to question, i will use Xen server


Je vais posé la même question en français. Selon les réponse que j'ai obtenu à date, je ne peux pas partager un LUN parmis plusieurs serveur. Je ne comprend pas très bien pourquoi je ne peux pas le faire, on parle de corruption de donnée. Pourtant lorsque je "share" un dossier sur un serveur, plusieurs machine peuvent écrire et lire sur le serveur en même temps. Pourquoi ce n'est pas la même chose avec un SAN ?

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"multire" ? –  Dennis Williamson Aug 24 '09 at 21:34
    
Which hypervisor, you don't mention? –  Chopper3 Aug 24 '09 at 22:29

2 Answers 2

up vote 4 down vote accepted

You can't present the same LUN to multiple hosts (either physical or virtual) without either clustering the servers in some way so that only one writes to the LUN at a time. Doing so will cause the volume to become corrupt as soon as both devices try to write to the LUN at the same time.

In Windows when you cluster only a single node of the cluster can access the LUN at any one time.

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Why when you share a folder in windows it's working but not with a SAN ? –  Cédric Boivin Aug 25 '09 at 19:03
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Because when you mount a LUN to both servers, they will both try to write a drive signature to the volume. As they both try to lock the volume the volume will become corrupt. Network shares work, because only a single machine is hosting the volume, and that machine allows other machines to connect to it, so the remote machines know not to attempt to write a drive signature because it's a remote volume. With a SAN volume the volume is a local volume to the server, so the server assumes that it owns the volume. –  mrdenny Aug 25 '09 at 20:05
    
So the better way to do my scenario is to mount a VM who mount the volume and share it to other server ? –  Cédric Boivin Aug 25 '09 at 20:59
    
I don't know much about ARR. From what I've read real quick you just need to setup a normal machine running IIS and ARR. It doesn't need it's own LUN from the SAN. –  mrdenny Aug 25 '09 at 22:31

I'm not sure what the shared storage requirements for ARR are but you can present the same LUN directly to multiple guest VM's if you install an iSCSI Software Initiator in the guest and configure the appropriate access controls for the LUN in your Equallogic Group Manager. As far as the Equallogic array is concerned the VM's are no different from any other initiator.

There will be complications though as the Hypervisor will generally not be 100% aware of the disks and that may affect things like Snapshotting\ Live Migration \ VM Cluster failover.

You should also check whether Microsoft will support such a set up - they support some clustering involving VM's but not all.

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I don't think he'll be able to mount the LUN as a volume in two Windows guests, simultaneously. One of the Windows guests is going to lock the volume for itself, unless he's using some form of clustering at the OS level. –  Kai Aug 24 '09 at 23:52
    
Absolutely true, I didn't make it clear in the answer but unless ARR implements an entirely new ( for Microsoft) cluster technique for disk sharing then concurrent access is not possible. –  Helvick Aug 25 '09 at 8:25

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