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RAID 10 queries

Hi EE,

I building a virtual environment for my client by virtualising his physical environment.

I'm opting for RAID 10 disk configuration for VMWare host server. I know RAID 10 has minimum of disks of 4. If you've used RAID 10 in the past either for physical or virtual environment, I have some questions below:

How many physical disk I required to give me better performance plus redundancy with no budget constraint?
What would be the capacity of each of my physical disk
After considering the above, once RAID 10 is configured using smart array controller from HP server, what would be the total size of my "datastore", i'm assuming it would show only ONE 'datastore" but performs mirroring and stripping for redundancy and performance.
VMWare host only accepts max of 2TB less 512mb of "Datastore" ? Is that means, regardless of the number of physical disks you have, the combine total should not EXCEED 2TB less 512MB?

I'm virtualsing the following physical servers:
File server with 250GB of data which is also acting as print server
Exchange with 150gb of data
Citrix server
Second DC

Thanks in advance.
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1 Solution
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
1. Numbers of disks

The more disks you have the better, more disks = more spindles = more performance.

2. Capacity depends on costs, make sure you purchase at least 10,000rpm SAS disks and not SATA.

3. That depends on what disks you purchase, but remember with HP, to purchase the optional Battery Backup Write Cache, and configure for 75% Write and 25% Read, using Smartstart CDROM Array Configuration Utilities which is on the bootable cdrom.

4. This has changed in vSphere 5.0 witgh VMFS 5. That's only applicable for vSphere 4.0.

Unified 1MB File Block Size. Previous versions of VMFS used 1,2,4 or 8MB file blocks. These larger blocks were needed to create large files (>256GB). These large blocks are no longer needed for large files on VMFS-5. Very large files can now be created on VMFS-5 using 1MB file blocks.

Large Single Extent Volumes. In previous versions of VMFS, the largest single extent was 2TB. With VMFS-5, this limit has been increased to ~ 60TB.

Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
But, yes if you are using vSphere 4.0 (ESXi 4.1), the maximum size of the VMFS datastore (array) that you present to the server must be less than 2TB (by 512bytes).

Configuration Maximums for VMware vSphere 4.1
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Personally, I would use 8 x 300 SAS, 10,000 RPM disks, in RAID 10, with spares.

So two hot spares, plus 6 x 300 GB

900GB Array, and I would split this into two datastores, because I do not like large datastores.

450GB - Logical drive 1 VMFS5 datastore1
450GB - Logical drive 2 VMFS5 datastore2

So ESXi would have two datastores of 450GB each, on a fast RAID 10 Array with 2 hot spares, using BBWC, configured as 75 write, and 25% read.
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mcse2007Author Commented:
Thanks Hanccoka

The spare one, would they be on 'standby' mode in case one disk has failed?

ThIS below talks about RAID 10 http://www.sohoconsult.ch/raid/raid10.html

Building on from your example, using the concept from the above link, if we have 8 disks, it would go as follows:

3 will perform mirroring
3 will perform stripping
2 will be spare

With 10 disks
4 will performing mirroring
4 will performing stripping
2 will be spare

With 12 disks
5 will performing mirroring
5 will performing stripping
2 will be spare

Sorry to asked these quetions, my experienced is limited to RAID 5 only.

Also, I'm intrigued about splitting the 900GB Array, how would you split that into two 450GB  'datastore' in VMWare?
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Yes, when you create the array, you can speciffy hot standby disks, should a disk fail in your RAID array, the spares will automatically be used in the array, and rebuilt using the spares.

Yes, that is correct. You do not have to use RAID 10, but it's the faster for READ and WRITES than RAID 5.

Yes, we personally do not like large datastores, ALL eggs in one basket, if an Admin deletes or destorys a datastore, not all is lost!

Umm to you. (performance is the same, because it's on the same Array)
mcse2007Author Commented:
Thanks again.....Now I'm getting confident using RAID 10.

I'm still not sure how would you split the RAID 10, with 900GB Array into 450GB - Logical drive 1 VMFS5 datastore1 and 450GB - Logical drive 2 VMFS5 datastore2, through VMWare?

Couple of points to make:

If you only have 2 disks mirrored the Array Configuration Utility will still call it RAID 10.
You can have multiple logical disks on one array with Smart Array controllers, e.g. with an array of 6 disks you can have 3 RAID 10 logical disks and 4 RAID 5 logical disks on it if you want. That's a bit excessive but it can be useful to slice the array that way to avoid having very large LUNs.
mcse2007Author Commented:
Appreciate it.
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