New VM Infrastructure- SAN/LUN Considerations

[StarTrek4U]

I recently came on as the Network Administrator for my current employer and after assessing the sorry state of affairs the network was in set out to drag it into the 21st century (kicking and screaming in some cases, lol). I've completed upgrading my network infrastructure and now am working on my server infrastructure. 2 days ago I just plopped down a pile of money for a sweet new virtual infrastructure; 3x Dell R710's /w 32GB RAM ea, 6.4TB Equallogic SAN, vSphere Advanced, etc.

I've set up a virtual infrastructure before however when I did it last time I got some bad advice on the SAN/LUN config which I think caused some performance issues later on as we loaded up our hosts. I'm initially going to virtualize about 12 machines but that number will most likely double within a year. This includes SQL and Exchange '07 in addition to the domain controllers, file & print servers, etc.

We're not a huge shop however I'm wondering what the best way to carve out LUNs on the SAN would be, it will be filled w/ 16 10k SAS drives. I'm pretty sure I don't want to make one big LUN out of it however I also want to have some room to grow and add VMs to a LUN, change/add disk if needed, etc.

So my question is what do you guys do? What's best practice, etc.

 

[lopoetve]

There's no hard and fast rule, except don't do one ~huge~ volume with everything, and unless you want to manage it, don't do one lun per VM.

Mixed, middle sizes with 5-10 vms is a good place to start. If you have no performance isuses, make bigger ones with more vms. Only testing can show what the array can handle per spindle/lun/volume.

Exchange should probably use RDMs for the main volumes - it likes that, and keeps contention down. SQL can benefit from it as well, if load is high enough.

 

[sabregen]

LUN sizing is going to require you to take inventory on your current disk usage. Are the to-be VMs already VMs on another platform, or will this be a P2V migration? If you're going top P2V them, I'd see what you're currently using, and plan for some growth, according to your business needs.

I would say 256GB chunks for the VMFS store, and I personally don't like going over 1TB per VMFS, if I can help it. Don't know if you need/want a VMFS3 ISO/mountable repository for your guest VMs, but it's worth keeping in mind.

I'd RDM on Exchange, SQL, or Oracle primary volumes. The rest might as well be VMFS3. Keep in mind your spindle counts, and RAID levels will affect your performance, as well. If I am reading your specs right, you've got 16x 400GB drives. You'll have to do your own sizing with growth planned in. Don't create VMFS3 stores that will be instantly filled. It would be better to spread them out, across as many spindles as possible. Also, VMFS3 volumes need 10% overhead to keep from bogging down, so keep that in mind.

 

[geiger]

Definitely try to separate the high I/O from the app/print stuff.

Just as a sanity point, do you plan to have a physical AD DC?

 

[nitrobass24]

I wouldnt make just one Huge one, but the EQLs do thin provisioning so I would cut yourself out a too small LUN especially for something like exchange.

Those things get big fast if your not careful.

 

[StarTrek4U]

That's good feedback, I'd forgotten about RDM until it was mentioned here. I suppose I was more curious if there was a best practice which doesn't seem to be the case. Based on what I've read it seems like RDM is a good idea for Exchange and SQL, VMFS for the other systems. If I have a File Server that's going to be allocated approx. 1TB, would RDM be a better idea or should I aggregate a few VMFS stores?

 

[geiger]

That's good feedback, I'd forgotten about RDM until it was mentioned here. I suppose I was more curious if there was a best practice which doesn't seem to be the case. Based on what I've read it seems like RDM is a good idea for Exchange and SQL, VMFS for the other systems. If I have a File Server that's going to be allocated approx. 1TB, would RDM be a better idea or should I aggregate a few VMFS stores?

Kinda depends on the seek pattern on the file server. Is it being used for roaming profiles or just normal file storage.

High volume database applications(exchange, mssql, oracle) would be ideal RDM targets.

 

[lopoetve]

That's good feedback, I'd forgotten about RDM until it was mentioned here. I suppose I was more curious if there was a best practice which doesn't seem to be the case. Based on what I've read it seems like RDM is a good idea for Exchange and SQL, VMFS for the other systems. If I have a File Server that's going to be allocated approx. 1TB, would RDM be a better idea or should I aggregate a few VMFS stores?

Single VMFS.