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2 VMs on a RAID10 volume, any problems with this?

Posted on 2010-11-24
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Dear all,

I am going to order a Dell server to host 2 VMs
VM1- Windows 2008 R2 Std (or Ent.)
VM2- Windows 2008 R2 Std (or Ent.) + MS SQL Server 2008 R2 Std

VM1 is the web/app server, VM2 is the DB server. Both are for a Maximo implementation, there will be 4 users, but may expand a little bit in the future.

My Plan A would be like this
- Get a Dell server with 6 hard drives. RAID 1 (C: 146GB)+ RAID10 (D: 500GB)
Hyper-V Host will be installed on RAID1, the whole RAID10 will be the data partition of the Host.
Two fixed VHD will be created on RAID10. One for each VM. On each VHD, there will be two partitions C: and D: in each VHD, C: for OS, D: for data for VM1 or SQL DB and LOGs for VM2

Would this plan sound okay to you?

Here is Plan B
- Get a Dell Server with 4 hard drives to form a RAID10, 600GB
Make 2 partitions, C: 100GB and D: 500GB. The Hyper-V Host will be on C:.
The 2 fixed VHDs will be on D:. There will be 2 partitions on each VHD, one is for OS, the other is for data for VM1 or SQL DB and LOGs for VM2

Plan B will save us at least $1500 dollars, i think.

Do you see a problem with Plan B?

I understand there could be many options for my situation, but your "real world" experience would be "invaluable"!


Thanks
Jack




 
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Question by:techcity
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kevinhsieh earned 500 total points
ID: 34210704
I would go plan B, but I don't see why 2 drives should cost you $1500. I would make a few small tweaks.

When doing the RAID sets, make a a RAID 10 set of 100 GB (or less, I suggest between 40 and 64 GB if you aren't going to put other stuff on it), and then another RAID 10 set for the D drive. It's better to put a single partition on each logical drive, rather then partitioning the drive. Same thing for the VMs. There should be a VHD for each separate drive letter. Don't use a single VHD and partiton it as that limits what you can do afterwards. If you have only 1 partiton on each VHD, you can easily expand the VHD drive and partition on it, and you can attach the drive to another VM without bringing along the whole OS with it.

With Hyper-V R2, the performance difference between a fixed and dynamic VHD is very small, and I personally use dynamic VHD files for all of my machines. It makes backups and copies so much easier because while I may have given 40 GB to a Windows 2008 VM for the OS, the VHD file might only be 10 GB, which is a lot easier and quicker to handle. Make your VHD set to be a reasonable size, and monitor the free space inside the VHD. If it fills up, you can shut down the VM, expand the VHD, and then use disk management in the VM to extend the partiton to fill the free space on the disk.

Sound like your first experience with Hyper-V. I would install Windows 2008 R2 on the host and add the Hyper-V role. Hyper-V Server 2008 R2 is great, and it includes clustering and everything (for free), but it's a little bit intimidating if you have never used Server Core because there is no GUI, only command line.
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by:techcity
ID: 34210808
Thanks Kevin for the prompt comments!

- Dell T310 server is quite inexpensive but can only support 4 drives. If I need to install more, I will have to go for the next level T410. Therefore the price difference is not only 2 hard drives in this case.

- " Don't use a single VHD and partiton it"
It makes big sense!

- According to your suggestion, I will need at least 8 drives to make two RAID10 sets. So my plan B (4 hard drives) does not seem to fit.

- "make a RAID 10 set of 100 GB or less"
Could you please explain the purpose for this small RAID 10 set?

- Because MS SQL Server will be on VM, would that still be a small difference between a fixed and dynamic VHD?

- I experimented Hyper-V Server in the past, it worked well. But I like the Hyper-V role better, because it allows me to work on VMs from the physical server itself, rather than from a workstation remotely. Maybe not everyone agrees with me, but I feel this convenience is worth to pay more.

Thanks a lot!

Jack
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by:kevinhsieh
ID: 34210909
When you create the RAID set, you can make it smaller than the available capacity of the drives, which allows you to create another RAID set using the same physical disks.

The small RAID set of 100 GB or less is for the C drive to put Windows 2008 R2 on.

Comparison of disk types in Hyper-V R2 showing little difference between the various types.
http://clusteringformeremortals.com/2009/09/25/hyper-v-pass-through-disk-performance-vs-fixed-size-vhd-files-and-dynamic-vhd-files-in-windows-server-2008-r2/
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by:walter_christian
ID: 34212339
Plan A is the better plan

you do not want the read\write of your OS to disturb you VMs and depending on how much activity your SQL server will cause you do not want to be in a position where you went cheap at the cost of performance. On top of that partitioning does not provide you with any strategic advantage so why bother?

I would go with plan A even if I was not VMing SQL as it would be the most performance centric solution and I am all about performance
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by:kevinhsieh
ID: 34213889
We are talking about 4 users here, and cost is clearly an issue. Best way to improve performance is to add RAM to the SQL server, which is also the cheapest. Using 10K or 15K SAS drives over 7.2 drives will be more important than keeping parent partition I/O (which should be negligible) off the drives.
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by:techcity
ID: 34223691
Thank you both experts for taking time on my questions.
Jack
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