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Power Consumption

New in our HDD tests, this section offers the results of power consumption tests according to our own methodology. You can read about it in our article called Hard Disk Drive Power Consumption Measurements: X-bit’s Methodology Indepth. We can also add a few words about the specific operation modes in which we perform the measurements.

First of all, it is the start-up moment when the platters spin up and the heads get unparked. Second, we measure the consumption in idle mode when the drive is not being accessed but its platters are rotating and the heads are ready to work. And finally, there are two work modes: random-address reading/writing and sequential reading/writing. These are emulated by means of the appropriate IOMeter patterns.

Note that 2.5” HDDs, contrary to their 3.5” counterparts, are powered by the +5V line only and do not take any power from the +12V line. The currents below can be easily transformed into power by calculating their values by 5.0V.

Unfortunately, we couldn’t measure the power draw of the MHX2250BT, but we are going to compare power consumption of HDDs with different spindle rotation speeds in our upcoming reviews.

Now, let’s see how much power the four 250GB 5400rpm drives need. For each mode, except Start, the average value, accumulated for 60 seconds of measurement, is provided.

The following diagrams show the amount of power consumed.

The Hitachi proves to be the most economical drive at startup, its consumption current being only 0.72A. The Samsung needs 0.03A more. The HDDs from Western Digital and Fujitsu consume 0.78A each. Note that these values are higher than 0.5A which can be provided by the USB. No wonder that such HDDs cannot start up without additional power if placed into an external enclosure and connected to a USB port of a regular mainboard or notebook.

There are two pairs of HDDs in Idle mode: the Hitachi and Fujitsu have a consumption of 0.8W. The Samsung and Western Digital need 0.9W.

When processing random-address requests, the HTS542525K9SA00 is the most economical drive while the MHY2250BH and WD2500BEVS are the most voracious in read and write mode, respectively.

Every HDD, except for the one from Western Digital, has a higher average consumption current at reading than at writing. We guess it is due to the HDDs’ ability to accumulate and reorder write requests to optimize the route of the heads.

The Hitachi is the most economical at sequential operations as well. The HDD from Western Digital has the highest consumption of all, 2.9W both at reading and writing. Note again that this is more than the USB connector can deliver when it comes to using these HDDs as external ones. The excellent performance in most of the tests has the tradeoff of high power consumption. By the way, we’re talking about average values but there occur occasional spikes of supply current that are sometimes even higher than the values measured at the startup moment.

The HDDs have roughly the same power draw at random-address and sequential requests, except for the WD2500BEVS that requires much more power in the latter case although the heads are moving more actively at random requests. We guess the explanation goes like this: the heads unit of a modern 2.5” HDD is very light and requires little power to move. Some more power is spent to keep the platters rotating, but the main consumer is the processor that keeps the head above the track, works with the buffer and calculates the read and write strategies. That is, the certain reduction of power consumption from the shorter movements of the heads in sequential-request mode is negated by the increased consumption of the electronics due to the increased amounts of transferred data and the necessity to maintain the position of the head above the given track.

 
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