Virtual Machine Density and Hardware Ceilings

[wd300]

Can anyone give me some insight on what is a good rule of thumb for  the number of virtual machines per ESX host in a farm? On top of that I am also wondering what limits should be observed as to when your CPU and Memory use should be considered at its maximum.

We have (4) Dell R900 servers with 4 quad core procs in aeach and a 128GB of memory. We currently have around 45 vm's per host and the CPU and memory use hangs around the 40-50% range.

Any advice would be appreciated.

[RParker]

Can anyone give me some insight on what is a good rule of thumb for  the number of virtual machines per ESX host in a farm?

Depends on core type, how many.  but the REAL difference is the DISK.  CPU and Memory is irrelevant, DISK is most important.

Quad core can do 8 vCPU PER core (as a rule) which means VM's with a SINGLE CPU.  Memory of course is a limit which you can easily identify.  Six core processors (R910/R710) can do around 12-16 VM's PER core, same memory and CPU, but spindle count is the ultimate dependence.

SAS/SCSI is better than SATA, SATA MAY be OK for a few VM's but if you want performance go SAS/SCSI.

[wd300]

Yes I agree that disk is important as we are getting ready to replace our entire SAN. But there si only so much CPU and memory capacity from a ohysical standpoint on our ESX hosts. Currently all four hosts are around the 50% mark. My question is how high can that get before a new host should get added to the cluster.

[RParker]

My question is how high can that get before a new host should get added to the cluster.

Well you don't want it to go above 90%, actually 80% for cushion.. Otherwise your host will begin to swap, that's bad.

So if you see memory getting around 80% consistently, it may be time to add a new host.