RAID Configuration for vSphere

[JudedeDude]

I have been tasked with designing the RAID element of my SAN for my new vSphere infrastructure and hit a stumbling block in regards to how to design this.

The SAN is capable in having mix disk SAS and SATA and RAID sets of RAID 1, 5 and 10.

What I am seeing is mix messages from the vendor (HP) and forums on the net on how to utilise the SAN for virtual machines use.

Some forum’s recommend using RAID1 for the operating system of the virtual machines and RAID 5 or RAID 10 (depending on data use) for the application like SQL or Exchange etc. Keeping the OS and Application functionality on separate RAID Sets. Is this normal for anyone else and if so do you have a performance benefit from this or is it all hot air!!!?

Your thoughts appreciated

[Dave_Mishchenko]

Your post has been moved to the Enterprise Strategy and Planning forum - http://communities.vmware.com/community/vmtn/planning.  The Communities Help forum is for questions related to using the forum software. Dave User Moderator.

[AndreTheGiant]

It's usual to have different type of RAID for different type of workload.

But split a VM in multiple type of datastore may not be always a better idea: all OS on one datastore and all datadisk on another could be worst (from performance point of view) than have some VM on one and some on another.

Also IMHO I prefer have a simple solution with all VM stuff in a single folder instead of several different folders.

Andre

[ChrisDearden]

For most applications , keeping everythign on RAID 5 datastores is fine , though I have a coupel of RAID10 Store that I use for heavy sequential write loads like log drives.

nb. if you dont have the raw spindles behind the different disk groups , you may negate any performance gain from running differing raid levels.

[lowteck]

hey jude,

those recommendations look like they're for physical servers (not for vms running on SAN storage).

I would recommend carving out seperate LUNS on seperate raid5 disk pools(sata and SAS)

Run your I/O intensive VM's on your SAS LUNS and use your sata LUNS for evertything else.

low

[JudedeDude]

Thanks Low,

I was hoping someone could clearly say as to why I shouldn’t design the SAN for virtual machines VMDK’s to be located upon different RAID sets for example talking to a fellow engineer his argument for an exchange 2007 server should be the following.

OS on RAID 1

Database on RAID 10

Logs on RAID 5

I would say why don’t we place everything on a RAID 10 been the highest performance needed, therefore we simplify our management!?

Do you get a better performance using the above?

[lowteck]

hey jude,

your fellow engineer is correct in his recomendation for a physical exchange server raid setup( thats microsoft's recommended setup)

if cost were no object, then yes, we would all use raid10 diskpools (w/ 15k SAS drives) as it offers the best overall performance.

we currently run a exchange2k7 vm  on SAN raid5 sas diskpools and we saw our performance improve from the above physical raid setup.

i am part of the Andre the Giant posse and would heed his advice

low

[msemon1]

Your fellow engineer is basing this more on recommendations for setting up Exchange on physical servers which is correct. I would keep it simple and set your RAID sets on the SAN with RAID 5 and create VMDK's or RDM's for your servers to look like this:

C: OS                         VMDK

😧 Database                VMDK or RDM

E: Transaction Logs     VMDK or RDM

Something to look at if your are in the market for new SAN equipment, companies such as EMC have something called FAST and FAST cache which

dynamically allocates between SAS and SATA drives based on I/O. That way you can balance the performance and cost between your SAS and SATA drives.

[JudedeDude]

Ok Andre,

Therefore splitting the vm's into different RAID sets wouldn't have any performance improvement and cause an administration overhead. Is there any other reason why this should be avoided?

Thanks

[msemon1]

You may get a performance boost performance in optimizing you RAID sets like you are proposing. Is it worth the extra administration? That is the 50 dollar question. I am in agreement with Andre on not separting your VM's, configuration files, swap files on different LUNS. That can be an administration nightmere.