I am in the process of transiting to a new position, my old position we used large LUNs (500GB) then created the VMs on those LUNs until we were 85% full (rule of thumb for Swap space / snap shots). Now where I moved into they present each disk as a separate LUN. Beside the obvious of having a confusing file structure, is there any benefit to doing it this way? The environment consisted of many two node clustered boxes that have anywhere from 6 VMs to 16 VMs per cluster, and each VM has 1 - 4 individual LUNs carved out. Quite painful!!! I would love to be able to come up with a compleling reason to present large luns rather than sticking with the individual LUNs if there really is no real good reason. Anyone out there gone thru this...feedback is welcomed. And NO I was not able to go to VMWorld UGGGGGGG...!!!!
In our environment, we have 200 virtual machines in just one of ESX farm/datacenters. If we presented a LUN per disk then we would be at 400+ luns (assuming each VM has a C: and a
drive). This is well beyond the maximum of 256 LUNs per ESX host.
In our environment it is much easier to simply create many large 1TB LUNs and put many VM's in each LUN. That we can easily grow the size of the VMDK's inside these 1TB LUNs. If we start running out of space one of the 1TB LUNS we simply storage VMotion a VM to a different 1TB LUN. We have over 40TB worth of 1 and 2TB LUNs presented to our ESX datacenter.
In short if you are going to have a reasonable number of VM's I would go with the larger LUN's. (note our SAN backend is made up of CX3-80 and a CX-700), if you are a real performance freak, then you'd probably go with a more granular approach.
Generally, best practice is to create LUNs large enough to host 10 - 20 VMs per LUN. This provides a reasonable compromise between the high management overhead associated with the smaller LUN size and the potential for SCSI reservation issues with large LUNs. Typically, the only reasons to create a LUN per VM are: 1) you plan to use SAN-base utilities such as snapshots at the LUN level or 2) you need to create a cluster.
Ken Cline
Technical Director, Virtualization
TVAR Solutions, A Wells Landers Group Company
VMware Communities User Moderator
That is exactly how it was in my old position. I am looking for compelling reasons as to why or why not use small luns sizes. Aside from the 256 LUN limitation there is a performance gain by using smaller luns? What I am now supporting is about 43+ hosts the majority of these are in two node clusters, most of those clusters are the same hardware so I see gain by consolidating those clusters into 4 or 5 nodes.
Thanks
Dan
Please consider the environment before printing.
Another reasonof using moderate sized luns is just the proverbial not putting all your eggs (or rather vms) in one lun thing. The more vm you have, you would suffer more losses when the lun gets corrupted, which unfortunately does occur.
When you say "you need to create a cluster", you referring to a ESX cluster? Why would using a LUN per VM be beneficial for creating a ESX cluster" Or are you referring to MSCS cluster? Then I can see where this would make the difference. And I am not sure if I mention this but not only is it a LUN per VM, they have it even more granular by having 1 LUN per Drive partition. I am just not used to supporting such an environment has I have always worked with the larger LUNs w/ 10 - 15 VMs per LUN
Thanks
Dan
Please consider the environment before printing.
Hi Dan ![]()
I guess if you where using RDM's (in virtual mode ) you run a LUN per VMDK - could it be SCSI locking paranoia ? What sort of VM's are you running - I can see it making sence for situations where you where p2v'ing a big file server and just presenting the file server LUN's to a guest.
The biggest problem I can see you having is hitting the maximum number of presented datastores per host if you were to have a decent sized cluster with a nuber of VM's on it ( possibly why you are only using small clusters , which seems a bit of a waste of resources)
When you say "you need to create a cluster", you referring to a ESX cluster? Why would using a LUN per VM be beneficial for creating a ESX cluster" Or are you referring to MSCS cluster? Then I can see where this would make the difference. And I am not sure if I mention this but not only is it a LUN per VM, they have it even more granular by having 1 LUN per Drive partition. I am just not used to supporting such an environment has I have always worked with the larger LUNs w/ 10 - 15 VMs per LUN
MSCS...
Ken Cline
Technical Director, Virtualization
TVAR Solutions, A Wells Landers Group Company
VMware Communities User Moderator
