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TQ or Not TQ – That Is the Question

Western Digital announced that second generation Raptor drives acquired Ultra/150 Command Queuing (Ultra/150 CQ) technology. Is the so long-awaited revolution? In fact, the situation is not as simple as it might seem at first glance.

I have every right to state that WD740GD drive doesn’t process the commands with NCQ, i.e. it is not the native processing of the requests queue, which was officially announced in Serial ATA II: Extensions to Serial ATA 1.0a, revision 1.1.

If you remember, the PCB of our WD740GD still has a Marvell 88i8030 chip, which means that WD740GD is an ATA drive, which can be connected to the SATA controllers because it is equipped with an ATA-to-SATA bridge.

ATA protocol acquired support of requests queue processing a while ago, when they introduced ATA/ATAPI-4 specifications. But there was only one HDD manufacturer who implemented Command Queuing in the drives: IBM (see our article called The Last IBM Drive: Deskstar 180GXP HDD Details for details). This way Command Queuing in an ATA drive is possible not only theoretically, but also practically, and the hard disk drive manufacturers can definitely put it into life if they desire to.

So, assume that the new Raptor supports ATA Queuing. However, in this case a question rises: does Marvell chip understand a set of commands implementing ATA Queuing?

Let’s check Marvell’s site. This is what we find in the specifications for the chip (click here to go to Marvell’s page):

Supports ATA command queuing

Well, this is exactly what I was striving at. But wait, and who said that CQ should only be supported by the drive? If the controller doesn’t support queue processing then it doesn’t matter at all if the HDD supports it or not. Tagged commands will never come to the drive in this case…

Assume that the SATA controller we are using supports command queuing (since SATA 1.0/1.0a specification includes this support). Also we have a PATA drive on the other end of the cable connected via a special converter. In this case the SATA controller should work as a compatible device emulating the registers of a PATA controller. As a result, only initial PATA queuing can work in this case.

Now let’s check if the diagnostics software will recognize CQ support by our Raptor drive. We will start with a very new and not very widely spread FC-IOMark utility (if you can think of a better name for it, your suggestions will be most welcome :). We haven’t yet finished working on it, but it already can disclose a lot of interesting things about the hard disk drives we run it on. We are particularly interested in the following section:

WD740GD supports CQ with up to 32 requests queue depth! Well, here we can stop looking for the implemented command queuing support, as we have just found it :)

 
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