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Best Hyper-V performance with 6 hard drives?

Posted on 2011-09-16
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Last Modified: 2012-06-27
I'm in the planning stage for a new server for 10 users. The server will have 6 drive bays.

How should I build the array(s) to achive best performance with 6 x SAS 15k drives?

I need arrays/partitions/vhds for the following systems:

    Hyper-V host (Server 2008 R2 Enterprise Edition - not a domain member)
    virtual Server 2008 R2 + (second) DC / DNS / DHCP
    virtual Server 2008 R2 + Exchange 2010
    virtual Server 2008 R2 + SQL 2008 R2 (light usage)

Should I use a single RAID 10 array with two partitions (first partition: Hyper-V host / second partition: fixed size VHDs)

Or is it better to use RAID1 (2 drives) for the host system + RAID10 (4 drives) for all virtual systems (fixed size VHDs)?
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Question by:exexc
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by:Andrew Hancock (VMware vExpert / EE MVE)
Andrew Hancock (VMware vExpert / EE MVE) earned 50 total points
ID: 36549726
RAID 10 will give you much better read and write performance, across six disks, more spindles, more disks more performance, because of the higher bandwidth from all six disks.

It's always better to use as many disks as possible in a RAID 10 set.
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As for how you divide up the disk into partitions, for isolation, between OS and VMs, keeps the partitions less fragmented, but each partition still has the advantage of fast underlying RAID 10 storage.
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kevinhsieh earned 225 total points
ID: 36550097
I agree with hanccocka, but for what it's worth, you have way more IOPS than what you need for 10 users. Let's say each drive can deliver 130 IOPS (which is more like a 10K drive, but I am being very conservative), that is 130*6=780 IOPS, or 78 IOPS per user. From a database perspective, IOPS per user on Exchange 2010 should be less than 1 IOPS per user. You need some more IOPS for the operating systems and such, but you are planning on 1.5 15K SAS drives per OS for a 10 user environment with a light usage SQL server. You could sell you 6 15K drives, buy 3 10K drives and use a RAID 1 with a hot or cold spare and you would have money to help pay for backup, not to mention the savings of not having to power and cool the extra drives. In this same vein, hopefully you didn't purchase more than a single processor for this server. Each VM should get 1 vCPU. If you add more, you will actually take a small performance hit in the VM (not that you'll notice either way, but adding additional vCPU isn't going to help unless the VM is really CPU busy, which none of your VMs should be).
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by:servacc
ID: 36550347
Thanks for your warning. I will have a look at the IOPS subject and reconsider the amount and speed of the drives. I wanted them to be extra fast, because the hard drives always were the bottleneck of my previous Hyper-V setups.

Could you explain why 6 drives in RAID 10 will sextuple the IOPS of a single drive? Is there no "overhead" and only 3 usable drives for write operations?
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by:kevinhsieh
ID: 36550377
You are correct that each write IO will generate two physical writes to disk, but every read IO is only 1 physical read, and it is generally reads that slow down systems. In addition, write cache on a battery backed RAID controller will buffer any writes.
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by:Lester_Clayton
Lester_Clayton earned 225 total points
ID: 36554079
I know that this question has received quite a lot of responses already, but I thought I should also add my expertise and experience.

It is true that RAID 1+0 (commonly referred to as raid 10) will give you higher performance, but this won't assist you for the kinds of virtual machines you will be running.  IOPS is not about throughpout - it's about how many I/O requests you have at one moment, and a heavily used SQL server will demand very high IOPS to get the best performance.

Let's think about this logically - 4 drives operating in a single array means that you effectively have 1 spindle.  Each time you do a write operation, all the heads on the drives work together to place the data there.  if you're writing a huge stream of data, it can do this very fast - but most data access is not like this - especially in a SQL or Exchange environment.

My recommendation for your 6 drive array is to split it up as follows:

2 Drives - Raid 1 - with the Host Operating System, plus your (second) DC / DNS / DHCP server.
2 Drives - Raid 1 - with the Exchange Server
2 Drives - Raid 1 - with the SQL Server.

This would mean an even balance for the guests as well as host - and give your exchange and SQL server their own spindles to use.  Neither exchange nor SQL will interfere with each others IOPS, and your performance will not be impeded.  The host and other guest also has it's own spindle, which means that any memory swapping the host does - cannot affect the performance of Exchange or SQL.  The performance effect on the second DC would be negligible.
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Author Closing Comment

by:exexc
ID: 36565662
Thanks for your suggestions and representations. This will help me to do some more specific research.
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