Where should I use my faster disk array in a Virtual Machine? System or Data?

The current ESXi server I am building has access to 2 local data strores.  both consist of 2 drives mirrored.  The first pair of drives are 10k SAS (300Gb) .  The second pair of drives are 7k SAS (500Gb).

For my Windows SQL server I'd planned to put the system vmdk file on the 10k datastore (where my c:\windows would reside).  Then use a thin porivisioned vmdk on the 7k datastore for the D: drive and the SQL databases.
The same would apply for my IIS server - using the D:drive for the inetpub dir.

Would I be better doing this the other way round ?  So that I was using the faster datastore for the D: drives - the SQL and inetpub data respectively?
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Andrew Hancock (VMware vExpert / EE MVE^2)Connect With a Mentor VMware and Virtualization ConsultantCommented:
The 10k disks are double the IOPS that the 7k disks have.

I would install the OS on the 7k (it's only boot-up).

if you want performance, I would install SQL Database and Logs on the 10k.

But checkout the performance for yourself using the following:-

1. Disktt

2. HDTach

3. CrystalDiskMark


 Characterize storage performance and correct: Storage Performance Analysis and Monitoring
You need to realize that no matter what you do, vmware will only make I/O go slower as it adds a level of encapsulation.  Can you go direct I/O, i.e, let the ESXi server itself directly control disk I/O by talking to a dedicated controller?

The most efficient thing would be to set up a NTFS file system with 64KB I/O for D:\, where the SQL is, and go with a smaller C:\ drive with default NTFS for the O/S & swap.  

If you must use vmware, then you should just make a single logical drive as vmware will do I/O in chunks based on the size of the pool anyway, so better to have one large pool so it can cache more I/O.   Remember, every I/O on C or D affects both disks, and you technically can do fewer I/Os on a combined C:\ drive due to the fixed block size that vmware will do

Summary: If using VMWARE,  just partition a single logical disk if it must be under control of vmware.  If you can dedicate the controller to the VM, then split the volume into 2 partitions, and you will be much better off.
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