Question on NFS Performance

compdigit44 used Ask the Experts™
We us NFS as our storage protocol and have seen very poor performance on our VM’s from time to time. On our SAN, the average latency is around 2 – 4ms which is ok. What I have observed is when our host our pegged at 95 – 100% CPU usage, our DAVG time goes up to 15 – 25ms. With that being said is the following state correct. With file level storage when the host is CPU constrained it will cause delays in the NFS calls to the SAN which in turn causes poor performance. In short, the CPU usage on the host has a direct result on NFS performance. This is not the case with block storage though correct?
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Kenza CohenIT Solutions Provider

Hi There,
Everything has its drawbacks obviously though with Block Storage you can go for the iSCSI route, generally high CPU Usage can affect both NFS and Block Storage.

You can see a comparison to help you formulate your own decision here:

VMware Storage Protocol Comparison White Paper

Also due to Design Block Storage is designed for High-Performance

Hope this Helps,



So my conclusion was correct? Also is block storage i.e FCoE or FC using a hardware adapter card i not as affected by high host CPU performance?
IT Solutions Provider
With NFS you will generally find you are constantly opening tunnels to the NFS and it is persistant however with block it is a persistant local connection so you should get better physical performance on the host OS.
Andrew Hancock (VMware vExpert / EE Fellow)VMware and Virtualization Consultant
Fellow 2018
Expert of the Year 2017
If you offload using FC or FCoE or iSCSI HBA - the CPU over head is gone!

Software iSCSI CPU is doing the encapsulation!!!

Also depends if Storage Device is native NFS or Block!

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