LUN sizing and max VMs per LUN

[GlennL10]

Consider a fiber channel SAN (EMC CLARiiON for example), and the limits around SCSI reservations, queue limits etc. per LUN.

What are you guys doing with regards to the number of VMs you are placing per a LUN?

How about the max sizes of your LUNs (in vSphere 5.0).

I am interested to hear your thoughts, advice and recommendations around this.

[sparrowangelste]

i think most people do either 500gb to 1tb luns, with some in between.

[GlennL10]

What are you doing in your environment?

[cabraun]

My preference has always been to use 500GB LUNs for datastores and a maximum of 10 VMs/Datastore as that, in my opinion has offered me the best performance and most flexability.  If any VM requires more than 400GB for a single volume than I have always given those VMs RDMs for that volume.

Of course every environment is different so YMMV but since you asked, I thought I would provide my input.

[GlennL10]

Thanks for taking the time to reply.

[mcowger]

Also, which Clariion/FLARE version - EMC's recommendations vary based on that.

[GlennL10]

CLARiiON CX4-240 running the latest version of FLARE 30.

[mcowger]

In that case, EMC's recommendations are a little different.

If you have VAAI, we have no specific value to recommend - use whatever makes sense from a protection and IO performance perspective.  With VAAI enabled, locking performance is no longer a limiting factor

If you DONT have VAAI, then the ~500GB guidance remains.

[GlennL10]

We do have VAAI.

I'm interested in the 500gb limit though, where can I read more about this, are there any blogs/official docs/helpful URLs that talk about this?

Thanks for your replies.

[mcowger]

Its not a limit, its 'guidance'.  We'll happily support you all the way up to the limits (16TB for Clariion), but its where we've seen the best results.

Our papers recommending 500GB are a little tough to find at times because we wrote them so long ago, but I will see what I can find.

[david615]

People recommend 500GB size on non-VAAI storage because there is high possibility that you will have larger number of VMs in are larger storage to utilize all the space.  If you have too many VMs running in a VMFS storage, you will run in to performance issues.

However, not all environment is same.  You need to get average size of your VM and think about how many VMs you want to have in your LUN.  For the argument sake, let's say average VM size is about 200GB and people are consumming most of the allocated storage space in the VM.  You don't want to have 500GB LUN in this case. You may want to have 2TB LUN to avoid provisioning too many smaller LUN.

David