November 2011
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ArcGIS Server on VMWare – Test results

With the County moving more and more toward virtualization, I found this very nice document discussing some testing that VMWare and ESRI did to test virtual vs. physical machines.

Esri ArcGIS Server 10 for VMware Infrastructure (.pdf file)

It includes some very nice benchmarks.

Some quick takeaways:

  1. Doubling the number of cores doesn’t appear to double capacity.  A single 4-core machine provides 73% of the capacity of an 8 core machine in terms of transaction capacity, not the 50% you might expect.
  2. Virtual machines, if configured correctly, will have similar capacity to physical machines (52,344 vs. 56,574 transactions per hour for physical and virtual setups, respectively).
  3. The optimal setup for virtualization causes issues that may well impact the viability of virtualization.
Let me explain #3.
A physical machine with 8 cores means one installation of the OS, one hard disk supporting the environment, etc.  The optimal virtual machine setup has 8 virtual computers, each with one  one virtual CPU (vCPU).  One machine runs the  ArcGIS Server SOM, which distributes mapping requests to 7 machines (each with 1 vCPU) running the SOC.
Basically we will now need to license, maintain, patch, and deal with 8 different machines as opposed to one.  Imagine having to install ArcGIS Server Service Pack 1 on 8 machines instead of just 1.  Theoretically with virtualization you just do it once and then recreate the images, but with each server requiring a different name, this may not be feasible.
One very much hidden piece to this covers the disk space.  Each virtual server would need to have space for the Operating System, ArcGIS Server, security, etc.  Let’s say around 100 Gb.  That means that we would need to have 800 Gb of space to run this.  Most virtual environments charge for disk space – rates vary, but per Gb charges are not inexpensive especially on fast SANs that are used for this type of stuff.
Even with costs for storage going down, it’s not free.
So – as we expand we’ll do a hybrid model – getting some physical and some virtual machines.  We had major problems with virtual machines in the past, and have transitioned back to physical.  I am going to be more careful this time.   Virtualizing machines generally sounds good, but do it carefully.

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