Optimal LUN Size for VMWARE


I asked my storage team to provide 5 LUN's with 2TB each for File Server purposes. The said they only provide 1TB Lun's because of performance metrics and VMWare Limitations. We have an IBM V7000 brand-new FC Storage with SSD disks and run VMWARE ESXI 5.1.

Each LUN will have just one datastore consuming 80% of its capacity.

What are your opinion on this matter?
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Paul SolovyovskySenior IT AdvisorCommented:
Typically you want to make the Datastore the size of the LUN but that depends on vendor recommendations.  1TB LUNs are a good choice, the smaller the LUNs the better performance may be depending on I/O per VM, we normally create 500GB to 1TB LUNs as standard.  vSphere 5.1 allows you to create datastores up to 64TB so depending on what you're using for, VMs per datastore, etc.. 1TB is typical size in most environments.

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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
We create LUNs between 500 - 800GB.
Hi garconer,

My understanding is VMWare ESXi 5.1 has a max of 2TB - 512B
See http://www.vmware.com/pdf/vsphere5/r51/vsphere-51-configuration-maximums.pdf

Now there is a speed issue for sizes over 2TB
See http://longwhiteclouds.com/2012/09/17/the-case-for-larger-than-2tb-virtual-disks-and-the-gotcha-with-vmfs/

Your storage team should be fine with the 2TB luns being allowable. I think you will find the issue is the performance side of things.  Just a quick reaction is the SSD's should be fine, but it's nice to know before jumping into something and getting a nasty surprise.  

My personal experience is some storage people don't understand SSD's as opposed to HDD's and advice caution based on old technology performance.  But please, don't assume your storage team are ignorant of the issues surrounding SSD's. The V7000 has some performance specs here. https://www.ibm.com/developerworks/community/blogs/storagevirtualization/entry/configuring_ibm_storwize_v7000_and_svc_for_optimal_performance_part_26?lang=en
You need to work closely with them around 2 performance metrics, iops and throughput.  IBM should be able to provide both on your new storage for it's intended configuration.

IBM have some iops applications in this document.

Can I suggest a test scenario so everyone is happy with the results, before jumping in the deep end.

In Christ Jesus,
Paul SolovyovskySenior IT AdvisorCommented:
In vSphere 5.1 the VMDK size is 2TB - 512B but the Datastore size is up to 64TB if you take a look at the min/max guide.  RDMs (virtual) is still 2TB -512B but physical can be up to 64TB

The main issue with larger Datastores is the increase in the number of VMs and SCSI 3 locking, typically 20 to 25 VMs max. is what we use per datastore to keep the SCSI locking becoming an issue.  

Best way to check for IOPs on VMs is to use vscsiStats commands via esxcli
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