Questions[lun](server)

I am working on setting up our vSphere 5 environment. With vSphere 5 you can go > the 2TB VMFS datastore size that you were capped at with in 4.x, etc. What size datastores are people using and whats a good way to determine the correct size?

My environment:

Hosts: I will be using 6 hosts (2 CPUS per w/ 6 cores per) = 72 cores. 192GB RAM per host = 1152GB RAM.

SAN:

VNX5500 with 35TB storage. This is tiered so it has a mix of SSD, SAS, NLS drives.

I saw someone use a formula someplace that looked like this:

(disk pool capacity – 10% free space) / total processors = datastore size

Does that look right? I may setup different levels of pools on the VNX, maybe gold/silver/bronze (which would basically be aimed at a SLA). So using this formula I would have a gold pool of lets say 10TB.

So thats (10TB - 10%) = 9TB (9000) / 72 = 125 so is that 1.25TB per datastore? And I would end up with ~7 datastores on 10TBs of space? Since VMware is aiming at easier managment through few objects, being able to go over 2TB per VMFs 5 DS now this doesn't look right to me?

Any help at all sizing my datastores would be much appreciated.

I have HP P2000 + XenServer solution working. What I'm thinking about is how to create LUNs for 20 virtual machines. Separate LUN for every VM ? It gives me ability to backup the specific virtual machine, however 20 vm = 20 shared storages in XenCenter and moreover I'm afraid of manageability of these LUNs or am I wrong ? Or I can have one bigger LUN for 20 VMs. What is the better option?

Both seem to be a virtualization layer on top of physical disks. I'm having a hard-time understanding each of them and the difference between them.

Obviously there's an infinite variety of ways of carving up your raw SAN LUNs to provide VM boot and data vDisks - but what methods do you use, what are their pros/cons, and are there any good 'best-practice' docs you've come across (other then the very generic VMWare ones I mean). Thanks in advance.

Its standard practice to separate log and data files to separate disks away from the OS (tempdb, backups and swap file also) Does this logic still make sense when your drives are all SAN based and your LUNS are not carved of specific disk or raid sets -they are just part of the x number of drives on the SAN and the LUN is just space allocation