Best practices for LUN sizes.

[vwman]

I am looking for the "official" vmware best practices on the best size for a storage LUN. We were told by a consultant about a year ago that 250GB was the best size for performance, but am wanting to create larger LUN's.

We are currently running ESX 3.5 on all of our servers and using EMC Clariion for storage. All of our servers connect using 4Gb FC to the EMC.

I know that the maximum LUN size is 2TB, but is that optimal?

Thanks

vwman

[RParker]

There is no such thing as a "set" LUN size. It depends on size of the drives, how many drives, how big your VM's are, and the number of VM's per LUN. 250g is rather small, VM Ware recommends between 500G and 1000g depending on what you are using them for. The biggest part is the number of VM's per LUN, you dont' want to go over 20 VM's. The number of spindles determines performance.

The more hard drives (spindles) the better.

[vwman]

Thanks.

Do you know how ESX will behave if we increase our existing LUNs from 250GB to 600GB. The LUNs can easily be expanded from the Clariion side. Will the ESX hosts recognize the new size? Is a reboot required?

vwman

[esiebert7625 · Accepted solution]

I think you'll generally find most users create a max of 500-600GB LUN's, higher then that some people use RDM's instead. There is not much performance benefit to using RDM's. Your storage performance will be most effected by how you architect your LUN's on the SAN, for example spreading your LUN's across more disk spindles and using multiple RAID groups split up by controllers. Below is some good reading on this...

LUNS - http://www.vmware.com/community/thread.jspa?messageID=333672

LUNS Size - http://www.vmware.com/community/thread.jspa?threadID=36725

Smaller LUNS or Larger LUNS - http://www.vmware.com/community/thread.jspa?threadID=90203

Larger LUNS = More Disks = More Performance - http://www.vmware.com/community/thread.jspa?threadID=84843&tstart=0

SAN Configuration Guide - http://www.vmware.com/pdf/vi3_esx_san_cfg.pdf

SAN System Design and Deployment Guide - http://www.vmware.com/pdf/vi3_san_design_deploy.pdf

Eric Siebert

VMware Communities User Moderator

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[cmanucy]

Although you can expand a VMFS with extents, this is not recommended.

If I were you, I'd just create new LUNs and copy the data to the new home. You might be down for a bit while doing this, but it's far better than dealing with the wrath of an extent gone bad.

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Carter Manucy