Optimizing SAN/RAID disk layout?

[hutchingsp]

I'm being a bit cheeky here as this isn't actually to use with our ESX cluster, but this forum is full of very knowledgeable people and I guess the basic principles hold true whether it's for ESX or, as in this case, for use with a dedicated physical machine.

So now I've done the buttering up, here goes:

Basically it's a PE2950 connected to a fiber AX4 SAN across a pair of switches with 4gb HBA's.

I have 10 physical spindles (after global spares), which are 400gb 10k SAS.

My initial need is basically to have 2 separate areas, "Users" and "Departmental Data".

My first thoughts were to simply create 2 physical RAID5's of 5 drives each, giving around 1.4tb of useable space for each area, now I'm also thinking single physical RAID5 carved into several virtual disks?

Predicting growth is impossible as it boils down to different departments will take on projects that may or may not require more space etc. so I'm not able to plan too much forward, other than that the intention of the SAN is that it should make provisioning storage a lot simpler.

However I also want to use Windows Shadow Copies so I also need to decide

a) whether to create a partition for this at the OS or SAN level?

b) what size?

Naturally Shadow Copies are just to save reaching for the tapes whenever anyone deletes anything so we don't need to have them going back especially far, but the farther the better.

I'd like to take copies at something like 10am, 2pm, 6pm, I think!

I'd appreciate any input on what you guys do please as it's one of those things where it's so easy to just go with what sounds right and end up with a couple of tb of data that isn't stored optimally.

[RParker]

You should setup 1 big RAID taking advantage of the 10 disks, better spindle speed.

Then make 4 LUNS of 1TB each, and make 1 for user data, another for departmental, and that last 2 for whatever.

That should give you good performance, and you will be in pretty good shape for LUN size.

[hutchingsp]

Thanks, that makes sense as one approach - I'm thinking 2x1tb for Users and Data, perhaps 2x100gb each for Windows Shadow Copies and that leaves around 1.1tb spare for a third volume as and when it's needed.

What I'm not at all clear on is the pros/cons of SAN partitioning vs. OS partitioning.

For example to acheive the above I would create a single physical disk group. Then I could create 2x1tb LUN and 2x100gb LUN and assign them to the server, or create 2x1.1tb LUN and partition it through Windows into 2tb + 100gb, or have a huge single LUN and create Windows partitions etc.

I guess the biggest benefit is that by using SAN LUNs there is more flexibility so far as migrating and expanding volumes than there is through Windows?