High CPU Usage in VMware Guest may NOT be CPU Problem

Hi CPU usage in the VMware guest may not be caused from an overloaded CPU.  It may be from a DataStore that is too slow.  Check the performance tab in your VMware client and see if that too is showing high CPU utilization.  If it isn’t, consider the speed of your DataStore.

We recently moved a VM from a RAID 5 with 3 slower SATA drives to a RAID 10 with 6 SAS 15k drives and with no other changes to the VM configuration and the machine performance has increased dramatically.

The problem appears to be caused by a backup writing files to the disk, which backs up the processor causing it to run at near 100% utilization waiting to be able to move on to its next task.  This will probably be most noticeable with database servers like Exchange and SQL.

Take this into consideration also when you are spec’ing out a new VMware server, as upgrading the DataStore disks to faster ones is not a simple job.  Include growth into your design; it’s always better to have an under-utilized server that is fast than one that is over-utilized and slow.

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