does NCQ affect disk I/O performance?

ehnde · November 2010

I'm studying storage solutions (this is all brand new to me) and also learning about virtualization at the same time. So much that I don't know!! I'm running my SATA drives in my ESXi server in IDE mode because my SATA controller isn't recognized otherwise. I've learned that when you use SATA drives this way you lose hot swapping capabilities (not worried about this) and native command queuing. Does the loss of NCQ affect disk I/O?

Any performance gain I can eek out of that box that doesn't cost money, I'd give it a shot. Rebuilding an ESXi install image is trivial...already done it to add support for a PCIx nic that isn't officially supported. If NCQ is important, I'd probably search around for drivers for my SATA controller.

I hope this post makes sense. I'm still incredibly ignorant on the subject of AHCI, SANs, virtualization, NAS and too many other topic to mention. Thank you for your advice.

tiersten · November 2010

ehnde wrote: »

Does the loss of NCQ affect disk I/O?

Yes. NCQ lets the drive optimise the order of requests by firstly allowing the drive to buffer commands and secondly allowing the drive to process those commands in whatever order it deems to be best.

No NCQ means the drive will rigidly follow the order of commands sent by the host. This means if the hosts requests blocks 5, 504, 3, 101 and 505 then it will process those in that order by seeking to each block in turn along with back tracking to the earlier blocks. If you have NCQ then it will buffer them all and then do 3, 5, 101, 504 and 505 in order. This is a simplified example :P

ehnde · November 2010

Thanks again Tiersten, you are always a wealth of information! Now to rebuild this ESXi image...

does NCQ affect disk I/O performance?

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