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The Idle mode goes next. As noted above, we give each HDD some time (about 10 minutes) to warm up after measuring the peak currents at the start-up moment. It is only then that we perform our next measurements.

This time the results are all understandable except for the suspiciously low consumption of the WD drive: the HDDs are ranked up according to the weight of the platter pack. You can note the similar consumption of the HDDs from Hitachi and Seagate and the somewhat better results of the Samsung.

The HDD from Western Digital requires one explanation. Having analyzed the results, I decided to listen to the HDD more attentively at the moment it switched from load to idle mode. So I created a simple IOMeter pattern that was bombarding the disk with random-read requests for one minute at a request queue depth of 1. After the end of this test there were no accesses to the disk and it should have been in Idle mode. I was keeping track of the instantaneous currents by means of an oscilloscope – it is easy to track the changes visually in Idle mode due to the linear shape of the graphs.

I found a curious thing. In eight to ten seconds after the processing of the last request, the HDD clicked softly and its power consumption on the +5V line dropped suddenly! The HDD seemed to park the heads and shut them down. A regular hard disk drive usually keeps the heads alive – they are in read mode and the HDD’s controller is reading service information from the platters (to stay on the track).

As opposed to this normal behavior, the Caviar GP has power-saving priorities and sinks into a slumber at every opportunity.

Is it good or bad? Yes, it’s good from a power saving point of view. And it is not good from a performance point of view. When the HDD is in such sleep mode and receives a read/write request, it has to spend some time to wake up (unpark the heads).

Now let’s see what we have in the Random Read mode.

Hitachi’s HDDs are not quite good here. Their power consumption is not proportional to the number of platters as compared with the competitor HDDs.  The Samsung is good again while the HDD from Western Digital is in the lead like in the previous test. I’ll try to explain later, using special utilities, how and why it needs so little power.

Now let’s see how many watts the HDDs can save by means of deferred writing.

So, the drives are all equal in this respect. Every model needs about 3 watts less in this test than in the Random Read mode. The HDD from Western Digital is the only one that cannot do this, but it consumes very little to start with. It would have to switch into deep sleep mode to save more power.

And now let’s check out the Sequential Read mode. The drives’ heads are not moving too much in this mode, resulting in a lower power draw compared with the Random Read mode. They still require quite a lot of power, though.

The Hitachi drives both notch 11 watts while the Samsung is slightly more economical than the Seagate models. The HDD from Western Digital is in the lead again.

The last test mode is Sequential Write.

There are no surprises here. The power consumption of nearly every drive has lowered in comparison with the Sequential Read mode. The only exception is the drive from Western Digital that has a somewhat higher power draw even. Perhaps it is due to the active operation of its electronics.

Summing up the power consumption tests, I can definitely name the winner. It is the Caviar GP from Western Digital. It has the lowest average power draw among the tested HDDs in all the test modes. The only exception is the Start-up test where the Samsung SpinPoint F1 won. The SpinPoint F1 takes second place in terms of power saving.

 
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