We recently upgraded the storage in our data center and migrated all our production systems to it. We noticed that in one machine (an HP_UX IA-64 Oracle database server for SAP), the CPU utilization started spiking up while the IO wait% was decreasing. Now the IO wait is 0% and all the CPUs are running at 100%(0% idle). Before, the IO wait was around 30-40% (average) and the CPU was around 15-20% idle(average). Can the increased throughput of the storage actually cause this increased CPU utilization?
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It certainly can. A definitive answer to the question of whether your CPU has gone up because of this would require more information, but in general, this is quite common and easily explainable.
Server workloads have to wait on a lot of things- CPU and memory, being local, often have to wait for things like network and storage. I've had applications go nuts becoming CPU bound after getting access to an SSD, for example.
It's very possible that your application is getting data back from the improved storage so much faster than before that the CPU has now become the bottleneck.
Basil
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An increase in storage speed can lead to an increase in CPU because more data can be fed to it.
But CPU is usually going faster than RAM nowadays. So it is strange that the CPU is going up to 100%. You are right to question this.
My guess is that something else has changed or your OS is not reporting the correct values.
Xavier Nicollet
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