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RAID config small hyperv setup

I'm setting up a new Windows Server 2012 R2 server.  The server has 3 x 600 GB 15K SAS hard drives in a RAID-5 array plus one hot spare.  My plan is to setup a Hyper-V host and then create two or three VMs (depending on whether the customer wants to pay to license the 3rd/4th instance).  The customer environment is relatively small.  Initially, there will be 6 users on the network with a 7th user connecting remotely.  There may be 10 or 12 users max within two years.  The workloads are Hyper-V by itself on the host O/S, Active Directory (guest O/S), Remote Desktop Services (guest O/S) and possibly applications/data in a 3rd guest O/S.  If we stick with only 2 VMs, the applications and data would have to go on one of the other two guests.  In my research of best practices, several people recommend putting the host O/S on a RAID-1 array and then putting everything else on a separate array, such as a RAID-5 array.  I'm wondering if this type of setup is really necessary in a smaller environment (i.e. 10 users) and if I would even notice a performance difference if I just did everything on a single RAID-5 array.  My server already has the RAID-5 array as well as Windows Server 2012 R2 Standard installed, and right now I only have a total of 4 hard drives.  I'd like to proceed with my original plan, but wanted to get some advice from the "Experts" on whether or not this would be a big mistake.  Thanks.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
We usually, see a

Data/VMs - RAID 5 (or better RAID 6) - RAID 5 has no place in production these days, as disks fail, RAID 6 gives better resilience!

Especially you find, if ALL disks are the same batch, they tend to fail all at the same time.....especially when you replace a disk in RAID 5, to rebuild, other disks start to fail, and your RAID 5 RAID array is worthless.

So RAID 6 better resilience!

see here, Statement from DELL!

AdamNVAuthor Commented:
I understand your concern about redundancy, and it's a valid concern.  Given my set of circumstances, however, if we assume for a second that I would be able to recover from a single hard drive failure in the RAID-5 array (either with the hot spare and/or replacing the failed drive), my question is really more about performance concerns.  How relevant is the following statement for the setup in an environment with 10 users:

"You must not store Hyper-V virtual machine files on drives used by the Operating System. It is because of the I/O operation. Drives, where the system files are stored, are accessed by the system processes continuously and this might cause delay in processing the Hyper-V tasks."
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
I would agree, and split the OS from Data (VMs).

on different disks, RAID Arrays. (not partitions!)
Philip ElderTechnical Architect - HA/Compute/StorageCommented:
Our base configuration is an R1208RPMSHOR with 32GB ECC, 1GB Intel RAID with NV Cache, and 8x 300GB 10K 2.5" SAS drives. They would be configured in RAID 6 with two logical disks:
 LD0 Boot: 60GB
 LD1 Data: 1.6TB

Since 300GB 10K SAS drives are very inexpensive we get enough storage but most importantly we get the IOPS we need to run any virtual environment.

RAID 5 is Anathema. That is, it is a no-no. Search "Punctured Stripe" for an idea of why.

The smallest setup that we have is on an X3470 with 32GB ECC and a 1GB Intel RAID and battery backup. That system came with six drive bays so we have six 600GB 15K SAS drives configured in a RAID 6. We had RAID 10 but one drive dropped and then about five minutes into the rebuild its pair dropped so we lost the server. RAID 6 all the way.

If the server has 6 bays then install 6 drives. If it has 8 then install 8. Maximum IOPS, even with 2 VMs, is the goal as the disk subsystem is almost always the bottleneck.
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