SAN Volume Best Practices - 1 VM per volume or several VM's per volume

Posted on 2012-09-09
Medium Priority
Last Modified: 2012-09-13
I have read several conflicting whitepapers on best practices for SAN volumes.

Is it better to have 1 VM per volume, or many VM's per volume?

I personally find it easier to manage SAN disc space & snapshots with 1 VM per volume.
Question by:Howzatt

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Heritage02Rider earned 500 total points
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by:Paul Solovyovsky
Paul Solovyovsky earned 500 total points
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Typically it is not a good idea to have 1 VM per volume as it become an administrative nightmare and you lose page file sharing where you typically save 10% on memory paging by vmware.

What we normally recommend is to have your datastores between 500GB and 1TB and spread out your VMs.  Large VMs may go on their own datastores as it provides room to grow and granular snapshots.

What type of SAN is in your environment, that may dictate the specifics.
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by:Andrew Hancock (VMware vExpert / EE MVE^2)
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We have clients that have both, 1 VM per LUN because it's easier for them, to manage, with the snapshot issue, and we have clients that have multiple VMs per LUN, LUNs sizes created between 500-800GB, apart from when they require a super-size LUN for VMs which require large virtual disks, of 2TBs, but generally these do not make good virtualisation candidates.

If you find it easier to manage with what you already have configured, I see no reason to change.

Different organisations have different setups.

Some also have individual LUNs, because it makes restore easier, and if a LUN gets corrupted or deleted, it's just a single VM which is affected.
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coolsport00 earned 500 total points
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A couple things come to mind:
First, how many VMs do you plan on having on this host? Regardless if using 1VM per LUN is what you're accustomed to, if you have a 'boat-load' of VMs, think about that for a minute. You're basically using 1 datastore per VM. As noted by @paulsolov, that can cause high admin (OPEX) costs to maintain & monitor so many datastores.
Second, you're not getting full ROI for your storage using only 1 LUN per VM. One of the main benefits of virtualization is consolidation and optimizing resources. Adding multiple VMs per datastore (LUN) does just that, in addition to using thin provisioning (if storage for your environment is at a premium).
Third, if you have different RAID volumes that you create LUNs on, you can have similar VM workloads on a single LUN within that RAID volume (group), again to minimize adminstrative overhead (less LUNs = less admin overhead)
Forth, you can create several LUNs on different RAID groups/volumes to have tiered storage based on SLAs for your VMs (apps). So, increasing LUN size and adding more VMs per LUN, yet creating different tiered LUNs based on SLAs gives a great balance of resource optimization and lessed OPEX cost.

There are of course benefits to using 1 LUN per VM, so you'll just have to weigh the cost-benefit of using 1 LUN per VM. In all honestly, it'll come down to what you wanna use, but "best practices" are to NOT use 1 LUN per VM.


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