Optimum disk- size for Windows OS in SAN

It all depends on what role the server will be.

A domain controller will not need the same capacity as a file server, or an SQL server.

In general, just for the OS partition, I prefer to have at least 40 GB, but no more than 60GB.  Remember, this is just for the OS.  You should have another partition for data.

Microsoft recommendations:
http://technet.microsoft.com/en-us/windowsserver/bb414778

I like to have the OS partition be a little extra large because of all the patches that need to be downloaded.  It is better to have it too large than to run out of space and have to grow the boot partition.

For data partition, how large a space can Windows 2008 R2 handle/address? Above link does not mention this.

awaggoner,
By extra large, do you mean 100 GB?

Microsoft recommends 40GB or larger.

I like to have it at least 60GB.  Drive space is pretty cheap now, and an extra 20-60GB probably won't make a difference.  Especially if you are running virtual machines with thin provisioning.  This doesn't actually use the extra hard drive space unless the VM needs it.

For the os partition, you can have up to 2TB but I would use 100 GB these days.

For data, the maximum if I remember correctly is 16 EB (exabytes) but that assumes 64k clusters.  But to go over 2 TB you need to use a GUID partition table disk (this is just defining the type of disk when you add it to the system - a GPT disk). Technically, you can use larger than 2tb for the c drive but its complicated to go so and not all hardware supports it.

Leew,

As I understand it, GPT can only be used for data partitions, not for boot, on intel/amd-based Win 2008 R2.
http://msdn.microsoft.com/en-us/windows/hardware/gg463525.aspx

Or, am I misreading it?

In my previous posting, I think I equated Itanium-based systems with UEFI-based systems. Both allow booting from GPT, but latter is intel/amd based, right?