Dedicated datAstores

[jasonwelch01]

Hello

We're In the process of migrating our vsphere 4.1 infrastructure to a new SAN (emc vnx 7500). I'm looking for suggestions/best practices regarding creating dedicated datAstores  for high IO virtual servers.  We have a number of high IO SQL servers and their vmdks reside on dedicated datAstores/dedicated LUNs on the array.  All of these dedicated LUNs/datAstores reside in a storage pool on the array as opposed to raid groups.  If I put the vmdks for these servers in shared datAstores as opposed to a dedicated one, am I risking these servers experiencing performance issues?  Are there specific circumstances when placing virtual servers in dedicated datAstores is recommended?

Thank you

[mcowger]

Are there risks?  Sure - everytime you share a resource there is a risk.  If you need to *guarentee* a certain minimum level of performance, you need to dedicate a pool or RG to these applications.

[jasonwelch01]

Thanks for reply.  Some of our high io systems will be in dedicated raid 10....for remaining systems sitting on shared datAstores, is storage io control a good solution to guaranteeing systems receive required io

[mcowger]

SIOC doesn't guarentee that IO happens, only that VMs get priority access under contention scenarios.  So its a very good start, but nothing but dedicated resource ever guarentees.

[jasonwelch01]

For any virtual servers that aren’t candidates for dedicated Raid 10, but have the possibility of producing heavy IO, do you suggest creating dedicated datastores/LUNs for these select VMs (SQL servers), specifically putting say the SQL servers Data & Log volumes on dedicated LUNs…Or is it considered good practice to still put these SQL Log/Data volumes on shared datastores/LUNs, as long as where cognizant not to put multiple SQL data/log volumes on the same datastore???

Jason Welch | Infrastructure Engineer

Information Technology

[mwpreston]

I guess it all depends (famous answer right?).

Depends on what you need for your workload of your SQL Server.  I believe best practices will still say to separate tempdb, sql data, and sql logs onto separate luns containing seperate physical disks....

So if you are worried about performance, you might want to do this....

Using shared storage always presents risks that one vm may affect the spindles of the other vms, but that's the chance you take to get the most out of your investments...

You could always start shared, but at the very least use seperate Virtual disks for these, if you notice you are taking a performance hit, the option to storage vMotion these disks to their own luns is there to help you...

I would also seperate place my os disk on a different controller than my data/log disks, and use pvscsi as a controller type for my data/logs/tempdb.  Also, I would probably consider using the VMXNET3 nic...There's also some advanced config you can do regarding Disk.SchedNumReqOutstanding = 64 and Net.vmxnetThroughputWeight = 128

Have fun :smileyhappy:

[mcowger]

Agree with everthing said here, esp. with the idea that svmotion can help you if you make a bad choice.

Also, its hard to estimate what 'heavy' IO means, because its so subjective.  For some of my customers, they consider 1000 IOPs to be heavy, but where I come from, that would be really light, and we'd say 20,000 IOPs was heavy.

How many IOPs are you driving, and how are your storage pools configured?