1 or 2 vCPUs for VDI?

[RudyG]

Hi all,

We're currently conducting a VDI POC - goal to run 40 (or 20:1) XP desktops across:

2 x BL460c (2 x Xeon 5140s, 16GB RAM)

ESX 3.0.1 (critical patches) / VC 2.0.1 (patch 2)

HDS SAN

I've read people achieving VDI consolidation ratios in excess of 50:1 - how many vCPUs are used for the desktops? I have 8 x 2.33 Ghz cores available.

-G.

[epping]

only ever use 1 vcpu, u will degrease performance if u use 2

[TomHowarth]

it is common practice to only give one vCPU to a VM, this will increase your density per server.

if you create 2VCPU VM's you are desiging in latency in that each VM will need two pCPUs or cores available to each request for resources.

[RudyG]

Cheers, we thought we'd try a stress-test last week (turning 10 machines on at once) and the system pretty much grinded to a halt for a good 10 mins.

Of course, I wouldn't be turning machines on in this way normally, but it was an interesting exercise.

[sgrinker]

epping already eluded to this, but we had asked a similar question to a consultant we had working with us on our project. Due to the time slicing that is occuring with multiple CPUs running on a VM... if a VM is configured for 2 CPUs, it may actually have to wait for a second physical CPU to become available in some cases before executing code. So if you have 20 VM machines configured for 2 CPUs on a 4x or 8x host, it could actually decrease your performance depending on what the machines are doing.

[williambishop]

You want funny, I put nearly 60 each on my blades.

On one of our last maitenance downs, we lost the san fabric for a few seconds. Assuming I had just lost my desktop vm's, I restarted all 60 hosts on each of the first 3 servers....Needless to say, bootup time was not great. It took somewhere in the neighborhood of 20 minutes.

Turns out that by the time I got to the fourth host, I realized that the sessions had not dropped a beat, they cached until the fabric was available again and then went on. You could hear my d'oh from a block away I imagine.

and on point... yes, for vdi, 1VCPU only!

[TomHowarth]

if we are quoting Simpsons, HA HA! no seriously thats a bummer

[jpratt_at_norwi]

I know this a very old thread, but can anyone speak to the issue of creating a vm with 2vcpu, then decreasing to 1vcpu? I understand it will still use the SMP HAL - is this correctable, or must the vm be rebuilt with 1?

thank you,

jamie

[mittim12]

You should be ok with switcing it back to the single CPU HAL though giving a preference I would rather start with the single.

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[TomHowarth]

if you leave the HAL as SMP, some weird issue surrounding performance may occur. the easiest method is to create a single vCPU guest and install your Gold master from scratch, if you are migrating physical machine into virtual, make sure you change the HAL in Device manager.

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Tom Howarth

VMware Communities User Moderator

[jpratt_at_norwi]

Thanks Tom, that is what I assumed since it does not give me the option to go back to the 'real' UP hal, but wanted to verify...

(modifed - this is xpsp3)

Regards,

Jamie