For a lot of people it has been a crazy week. Some of you might wonder why, some of you know what I'm talking about. VMware Partner Exchange 2010. With PEX coming up for many of you that means GTJD, GTJD? Yeah, Getting The Job Done! Being away for a week in my case means I need to wrap up project and answer a lot of emails before it gets out of control. That doesn't however mean that I don't have time to create a top-5…. This weeks list contains the all-star bloggers:

• Scott Drummonds – PVSCSI and Low-IO Workloads
  At low IOPS the CPU is doing very little work to access storage
  hardware.  In these environments it is simply not worth anyone’s time
  to implement and use a special driver storage driver.  But when 10-50k
  IOPS are streaming through the virtual SCSI bus, a new approach that
  halves the number of cycles spent on each IO will noticeably decrease
  CPU utilization.  This is why we created PVSCSI. The current design of PVSCSI coalesces based on OIOs only, and not
  throughput.  This means that when the virtual machine is requesting a
  lot of IO but the storage is not delivering, the PVSCSI driver is
  coalescing interrupts.  But without the storage supplying a steady
  stream of IOs there are no interrupts to coalesce.  The result is a
  slight increase to latency with little or no efficiency gain.
• Frank Denneman – Sizing VMs and NUMA nodes
  ESX is NUMA aware and will use the NUMA CPU scheduler when detecting a
  NUMA system. On non-NUMA systems the ESX CPU scheduler spreads load
  across all sockets in a round robin manner. This approach improves
  performance by utilizing as much as cache as possible. When using a
  vSMP virtual machine in a non-NUMA system, each vCPU is scheduled on a
  separate socket.
• Jason Boche – Configure VMware ESX(i) Round Robin on EMC Storage
  The answer was buried on page 88.  The nmp roundrobin setting useANO is
  configured by default to 0 which means unoptimized paths reported by
  the array will not be included in Round Robin path selection unless
  optimized paths become unavailable.  Remember I said early on that
  unoptimized and optimized paths reported by the array would be a key
  piece of information.  We can see this in action by looking at the
  device list above.  The very last line shows working paths, and only
  one path is listed for Round Robin use – the optimized path reported by
  the array.
• Scott Lowe – Using IP-Based Storage with VMware vSphere on Cisco UCS
  From the VMware side of the house, since you’re using 10GbE end-to-end,
  it’s very unlikely that you’ll need to worry about bandwidth; that
  eliminates any concerns over multiple VMkernel ports on multiple
  subnets or using multiple NFS targets so as to be able to use link
  aggregation. (I’m not entirely sure you could use link aggregation with
  the 6100XP interconnects anyway. Anyone?) However, since you are
  talking Cisco UCS you’ll have only two 10GbE connections (unless you’re
  using the full width blade, which is unlikely).
• Gabe – Licensing problems with VMware VIEW4
  The problem Jon was facing, was that it was impossible to just add
  those 20 (2×10) licenses to vCenter without assigning them to a host.
  Because, in our believe, there should just be 20 licenses in some sort
  of pool that each VDI VM would take one license from. It is possible to
  assign multiple hosts to one license so they can share the number of
  available VMs in that license. What you can’t do is have a host connect
  to more than one license, which in our opinion would also be feasible.

The server used was a Dell PowerEdge M710 with 2 x quad core Intel Xeon X5570 2.93 GHz processors, 72 GB of Memory, and running VMware vSphere 4. Two 4 vCPU VMs were created and configured with SuSE Enterprise Linux 10 64-bit. Oracle 10.2.0.2 was installed in the first VM. The second VM was configured as a SAP application server with NetWeaver 7.0 ABAP. In this two-VM configuration, the SGEN transaction was run on the app server VM which in turn accessed the DB VM during the processing of the jobs. The SAP_BW set of objects was used for this set of tests.

The first set of best practices applied were VMware specific. The second were specific to SAP and were made by adjusting the profile settings for the SAP application server instance. The final adjustment was to give the app server VM more resources. The chart below shows the results as each change was made:

There are several jumps in performance. The first is the upgrade to use the VMXNET 3 virtual adapter instead of the default e1000 adapter. In this network intensive application where lots of packets are passed between the app and DB VMs, the better performance of the VMXNET 3 adapter makes a big difference.

The other big jump in performance comes with the increase in the number of dialog work processes for the application instance. By monitoring the CPU utilization with "top" inside the guest, "esxtop" from the ESX console, and the SAP dialog queue (with SAP’s dpmon tool) it was clear that the VM was not working very hard with its initial configuration of 10 processes. By increasing SAP dialog instance work processes until the CPU of the app server VM was nearly saturated, the time for the SGEN job to complete improved greatly.

While the CPU utilization of the app server VM was high, the DB VM was still only about half utilized. To push more work over to the DB VM, the number of vCPUs on the app server VM was increased from 4 to 8 and the number of work processes was also increased to 40. This change resulted in another decrease in the SGEN completion time. In the vSphere Performance Best Practices Guide (page 21), it states that a VM with a number of vCPUs less than or equal to the number of cores in each NUMA node will be able to take advantage of NUMA optimizations and have the best performance. This SGEN workload is CPU intensive enough to get continued performance improvement even as the number of vCPUs (8) exceeds the number of cores in a NUMA node(4). However to really determine if this is the "best performance" another test would need to be run to compare a single 8vCPU app server VM with two 4vCPU app server VMs.

These tests show that applying both VMware and SAP best practices can make a big difference in performance. In workloads that are resource intensive, such as the SAP SGEN transaction, using the best performing virtual NIC and adjusting key application settings based on performance monitoring are key to achieving best performance.

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