Should NCQ be enabled for drives in raid?

[Neb]

I was in a discussion with someone that insisted that NCQ should be disabled on drives that are in a raid since the controller card knows the situation better and can do the NCQ itself. They cited as proof the fact that enterprise drives have NCQ disabled.

I'm fairly confused about the subject myself now, as I can't seem to find any concrete info online so I'm asking here in hopes that more experienced folks can answer

1) As far as I can tell and from searching, NCQ is a function that requires both the drive and controller to have it enabled (along with the corresponding driver support on the OS side); is this true or not?

2) Are enterprise drives shipped with NCQ disabled and what would be the reasoning behind doing so? Compatibility perhaps?

 

[mikesm]

Empirically, when running linux software raid, I would much better performance with NCQ off than on. That said, most consumer drives do a crappy job of implementing NCQ, and a bad NCQ is a lot worse than not NCQ at all when in RAID mode.

 

[C-rizzle]

Well, do some benchmarks before & after to see. B/c not all settings are universal one way or another. Sometimes, you have to test and see what works best with your hardware/software combination.

I wasn't sure about Volume Write Back Cache. So I tested it before (not enable), then after (enabled) and performance dropped A LOT with it on. So I went back to not enabled.

My tests were on 2 x 640Gb WD Blacks in Raid 1 on ICH9R.