Storage Arrays in VMware

Posted on 2011-09-04
Last Modified: 2012-05-12
All, we are in the process of planning our storage utilization on a VNXe connected to VMware 4.1 (maybe VMware 5). We are going to follow best practice by EMC and create a RAID5 for general use data and a RAID1/0 for the high performance items such as SQL and Exchange.

My question, when planning which datastores to use on my VMs should I put all of Exchange on the high performance or split them up? For example, my Exchange environment I have an OS disk and a DATA disk. Can I put the OS VMDK file on the RAID 5 and the Exchange DB/LOGS on the RAID1/0? I'm thinking I need to keep everything on the RAID1/0 because the OS will process the data and if the RAID5 is the bottleneck then having the RAID1/0 wouldn't do any good (performance wise).  Same question for my SQL servers.
Question by:pitchford
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Expert Comment

ID: 36482184
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Expert Comment

ID: 36482186
I would say it depends on total IOPS, number of users, etc..

We have setup Exchange on a VNXe in a RAID5 datastore with no issues and MS fully supports storage on SATA drives due to reduced IOPS requirements for Exchange 2010.  On the other hand if you have large amount of users it may be a good idea to put on RAID1.  I like to keep the OS and Data on the same datastore for simplicity but that's your choice
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Expert Comment

ID: 36482573
Exchange should be able to run on RAID5 as already mentioned. You can put different VMDKs on different datastores according to performance needs. For SQL, OS can be on RAID5, logs on RAID10, and database on RAID5 or 10.
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Expert Comment

ID: 36483179
paulsolov is correct - you are the only person who can say what your environment will require, we have no idea how busy your systems are.
For example, RAID10, shared by more than one system - each of which needs the maximum performance the physical disks can provide, will perform worse than many lightly loaded systems on RAID5.
RAID10 is only faster than RAID5 for writes *for the same number of physical disks*.
Think about which systems you're putting onto the pool/group of physical disks, and what their loading is and what times of day they'll be busy.
Also note that for the most part, you'll be writing to RAM in the storage processor, and not be talking direct to the disks. A few exceptions: if you write enough to fill the write cache and thus force cache flushing, or write a block of data that is larger than the "write-aside" value (usually 1MB).
The same is not true for reads, usually very little read-ahead cache is used - though EMC do have a clever algorithm to try and speed up access to sequential data for reads.

Author Comment

ID: 36485659
I think the point of my question was missed. I know the pros and cons of virtualizing Exchange/SQL. I'm looking to find out if it would be useless to put the data VMDK on the RAID10 if the OS partition is on a RAID5. I'm thinking my data would be if the data is capable of going 100 mph but the OS limits it to 50mph it would be pointless to build my data on something that is capable of doing 100mph.

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Accepted Solution

paulsolov earned 500 total points
ID: 36485983
I don't think it would make a difference to put the VMDK on RAID10 other than loss of storage.
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Expert Comment

ID: 36486571
Where the OS is stored does NOT affect IO to the other VMDKs that the VM is using. Each VMDK will perform independently according to whatever the underlying storage is for that VMDK. It makes sense to put the OS on slower, cheaper storage and the databases on faster storage.
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Expert Comment

ID: 36486898
back to my comment above, only YOU know how YOU have configured your applications. I'm not going to say much more on this question as it's closed, but if you don't configure your applications correctly they can really hammer the OS disk (think SQL server and where it puts TempDB by default...).

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