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Linear Read Speed

I used the good old WinBench 99 to draw the following linear read graphs (the pictures are clickable):


WD740GD


WD1500AHFD

So, the new Raptor X is almost 15MB/s faster at linear reading. This is a very big step forward! On the other hand, the common notion that a drive’s performance depends directly on its linear read speed is not exactly true. It doesn’t, and you are going to see that right in the next section of the review.

NCQ vs. TCQ

After all is said and done, the main and most intriguing feature of this review is the new hard disk drive’s support for Native Command Queuing technology.

Western Digital’s Raptor drives used to support only the so-called legacy ATA queuing. And WD’s market opponents would regard the word legacy as synonymous with obsolete or archaic , promoting NCQ instead. But you may remember that even that old and archaic technology did quite well in our tests.

But now that the Raptors have acquired support for the most progressive commands-reordering technology, the competitors cannot really blame Western Digital (except for the company’s growing profits :)).

The WD740GD drives support Tagged Command Queuing (TCQ) whereas the Raptor X features NCQ. The Promise S150 II TX2+ controller supports both the versions of this technology, thus giving an opportunity of an all-around comparison.

As usual, I use IOMeter to bombard the drive with a stream of requests to read random-address sectors while steadily increasing the length of the request queue. Thus, the controller has an opportunity to send independent commands to the drive (commands whose result doesn’t affect the queuing or processing of other commands).

The drive receives the controller’s command to read a random-address sector and puts it in the queue (a special buffer that can store a maximum of 32 commands) and then processes the queued commands in the order it thinks most advantageous for the user. The drive may be trying to reduce the average time of response to a request or to make the maximum response time lower, but this is the know-how of the programmers that are developing the secret algorithms to be written in the drive’s firmware.

My task is to send requests to the drive’s input and have some output from it. And then I’ll explain the output as best as I can. So, the next diagram shows the results of the three tested drives (two WD740GD and one Raptor X).

And what do we have here? Even the old WD740GD-FLA1 is far faster than the new Raptor from WD than the length of the outstanding request queue is over 16. And the WD740GD-FLC0 is even better than that – this one is just a wild drive, so fast it is!

Can it be that NCQ just doesn’t work in the new drive? Or maybe the controller doesn’t send it the “magic” commands? On the other hand, there’s a definite performance growth as the outstanding requests queue is getting longer and the graph has a characteristic shape at loads of up to 32 requests, too.

 
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