The problem of power consumption and heat dissipation in modern computer components does not need any special substantiations or introductions. It exists and should be somehow dealt with. It's especially critical with the present-day processors and video cards. But the object of this article is another computer element, critical to overheating — hard disk drives (HDD). Manufacturers measure off quite a modest range of operating temperatures — from +5 to +55°C as a rule (occasionally from 0 to +60°C), which is obviously less than in case of processors, video cards, or chipsets. Moreover, reliability and durability of these drives depends much on their operating temperatures. According to our research, increasing HDD temperature by 5°C has the same effect on reliability as switching from 10% to 100% HDD workload! Each one-degree drop of HDD temperature is equivalent to a 10% increase of HDD service life.

It goes without saying that servers and professional data storage systems pay special attention to cooling hard drives — drives are installed into special metal cages and cooled by fans. In such cages the HDD temperature stays within 30-40°C even under heavy load (sometimes it's even close to the environment temperature), which drives away all overheating concerns.

However, much less attention is paid to the problem of HDD cooling in more consumer-like cases, including personal computers (from hardware integrators or self-assembled), workstations, and even entry-level servers, to say nothing of growing increasingly popular "computerized" consumer electronics with hard drives inside (play stations, personal digital video recorders, etc). That's partially due to lower requirements to data storage reliability, partially due to economic reasons, and also because any additional fan makes a device noisier, which is very undesirable. The following two components grow especially important under these conditions:

1. Construction of HDD mounting in a case (relative to other active cooling systems, main airflows inside the case, and passive surfaces that channel the heat away relatively well — metal chassis); but still, our article does not deal with that issue, to be more exact it deals with a slightly different thing.
2. Heat dissipation of drives in various operating modes. That's what our article is about.

I hope there is no need to explain why the heat dissipation of a drive matches its power consumption from a PSU almost perfectly: if we dismiss minute mechanical work, performed by some ill-balanced storage devices by vibrating themselves and the neighbourhood (where they are installed), as well as the power of acoustic and electromagnetic (radio-frequency range) vibrations generated by the operating disk, there are no other ways the drive can transmit energy outside, except for the thermal form. And the only power source of a drive is electricity (we shall reasonably ignore heating from external sources so far ;)). That is we face a classic "electric oven" of a hard drive (the same also applies to a processor — CPU or GPU), it will interest us in this article only in this respect. :)

HDD Temperature Reading Mumbo Jumbo

Some users are too naive to think that all they need to understand everything about heat dissipation of a drive is to measure temperature of the drive during its operations or tests. They think that if they compare several hard disks by this temperature measured under domestic conditions, they could draw profound conclusions that one disk is cooler than the other, that is better and dissipate less heat. Several authors of HDD reviews even base their statistics on it, mistaking its validity and relation to the realities of life. Their readers buy a reviewed hard drive and expect it to keep below 42°C or, say, 47°C — that's because "computer gurus" reviewed it…

Why is it a delusion? Because taking correct readings, that is trying to judge about hard drive's heat consumption by its temperature, all the more to determine the real operating temperature of a given hard drive compared to other drives, requires at least knowing the ropes or helluva onions. :)

That is to ensure accuracy and validity of temperature readings with the measurement error within at least 1-2°C, you must put hard drives into a heat chamber, provide similar heat dissipation conditions (chassis mounting, air circulation), and read the temperature by an external sensor (that is not by the built-in one) at least at several surface points (temperatures inside hard drives can be interesting to only manufacturers, so we shall not analyze them). You must agree that organizing such measurements on a system basis even under conditions of a regular computer testlab is problematic at best — it requires special expensive equipment, rare labs can afford. Otherwise, the measurement error of all makeshift readings under improvised conditions or "system units" will be minimum 10°C, which reminds the notorious "average temperature in a hospital". Furthermore, under these conditions you shouldn't try to compare temperatures of various drives, differing by 2-5°C. It's utterly useless and even harmful, because it misleads credulous readers!

Moreover, if you possess a good heat chamber and other accessories to take correct temperature readings, the results obtained will also be useless to some extent for those who want to know what real temperature their hard drives will reach! That's because real systems channel heat absolutely differently and it cannot be calculated in detail. Conclusion: you'll have to put a given system unit into a large heat chamber (with specified airflow conditions) and take readings. If you risk taking these readings outside a heat chamber in a regular room, a large measurement error due to the drift of room temperature and local airflows will bring to nought the idea of such experiments. However, even if you manage to take these readings, you will not be able to tell for sure that the operating temperature of this drive will be the same in a different chassis, because systems may have quite significant differences in HDD cooling conditions.

Another question — what can be used to measure HDD temperature (if you still want to measure it ;)). It goes without saying that readings of the built-in sensor are absolutely unreliable! Yep, this thermal sensor may roughly guide you in everyday "consumer" practice (e.g., in order to be sure that your drive is not overheated above the safe limit), but these readings cannot be used to compare different storage devices! The fact is that different models have built-in thermal sensors in different locations so that they measure temperatures of totally different parts, which may have different operating temperatures — even in the same drive in different operating modes! Unfortunately, there is no common industry standard on this issue so far. So, if you are still keen on being informed on the real temperature of the hard drive case (specifications usually limit this very characteristic) and, all the more, comparing various drives by their case operating temperatures, you should use an external thermometer of the proper accuracy class.

Power consumption is the "correct" unit of heat dissipation

But enough of measuring temperatures — we are absolutely not going to do it in this review. :) That's because we shall take power consumption for their heat dissipation measure (see above). Moreover, power consumption turns out a much more flexible characteristic in this respect, because it allows to quickly obtain precise data on heat dissipation of a drive operating in various modes (from idle to seek, read, and write), which would have been problematic by reading temperatures. Moreover, you cannot use temperatures to measure for example start-up power consumption. Besides, it's much easier to measure power consumption than to read temperatures with a given degree of accuracy.

Thus, the most correct measure of hard drive heating is the electric power it consumes. But power consumption of hard drives is also important for us because power saving in modern computers is becoming an issue of primary concern. Power consumption of processors and video cards is growing, a couple of dozens of Watts in a hard drive against these nearly-hundred-Watt ovens does not seem so critical. But it depends: in case of a low end PSU (250-300 W), an additional hard drive (or even the simplest RAID) may result in the necessity to upgrade a power supply unit to a more powerful one. Besides, no one abolished the problem of high start-up power consumption – for example, the plain Barracuda 7200.8 may draw up to 2.5A from the +12 V line at start-up. Add 3 W drawn from +5 V to get the peak start-up power consumption of 33 W! What if there are two or three such drives in a system? In this case you should play safe and take a PSU at least by 100-150 W more powerful than processor+video+motherboard require. Food for thought.

So, the object of today's review is to compare power consumption and heat dissipation of modern 3.5-inch hard drives in various operating modes. We shall mostly review desktop models with Serial ATA and UltraATA interfaces, as the most interesting to the majority of our readers. But we'll also include some recent SCSI models as a reference.

Hard Drives' Specifications

As a reference, Table 1 contains power consumption data for the main HDD series, provided in their specifications. We shall start from the beginning. :)

Irregardless of specifications, you should be well aware that they are not a panacea and cannot provide complete facts of life: sometimes manufacturers specify only upper limits, sometimes – typical values, sometimes these figures have nothing to do with reality, if you compare them with the readings taken from these drives. Nevertheless, specifications exist and we should face them.

Another funny delusion - users often consult cases of a hard drive and fondly believe that the power consumption data printed there is true for a given sample of a hard drive ("this data is printed there for a reason!" ;)). Having compared these parameters with real figures, you will see that it's often not the case. Moreover, these parameters often mismatch even the specifications on these drives. It's often not so easy to understand the principles, which manufacturers follow to mark technical parameters of drives on their cases.

Contenders and Test Methods

We have tested 35 models of modern 3.5-inch hard drives from all major manufacturers. The drives are listed in the table with test results below. We used the following testbed configuration to measure power consumption of hard disks:

1. CPU: Intel Pentium 4 3.0C
2. Gigabyte GA-8KNXP Ultra-64 motherboard based on Intel E7210 chipset (the i875P with Hance Rapids 6300ESB southbridge and PCI-X bus)
3. RAM: 2x256 MB DDR400 (2.5-3-3-6 timings)
4. Ultra320 SCSI Adaptec AIC-7902B controller on PCI64 bus
5. The main hard drive: Maxtor 6E040L0
6. Power supply: Zalman ZM400A-APF, 400W
7. Chassis: Arbyte YY-W201BK-A

We measured the power consumption of hard drives in various modes: Idle, ATA or SCSI Bus Transfer, Read, Write, Seek, Quiet Seek (additionally, if supported), as well as Start. A package of these parameters renders the situation with HDD heating (a product of current and voltage gives the heat rate dissipated by a drive) as well as with its economy in the most complete way. Operating modes of a hard drive were controlled by the corresponding tests in AIDA 32 Disk Benchmark, read and write modes were measured "in the beginning" of a disk (on the most frequently used outer tracks; power consumption on inner tracks is usually lower). The tests were carried out under MS Windows XP Professional SP2. The hard drives were tested non-partitioned. Before the tests, we warmed the hard disks for 20 minutes using a utility with active random access.

We measured the +5 V and +12 V draw (accurate voltages at the output of the above mentioned unit were +5.08 V and +11.82 V) simultaneously with two digital ammeters of the 1.5 accuracy class with the resistance below 0.15 ohm (including the leads' resistance). The refresh rate of readings was approximately 0.3-0.4 sec. The table provides average values for several seconds (current fluctuations usually didn't exceed 30 mA), except for the Start-Up current (the table contains maximum values).

Test results

Our readings are published in Table 2. The last column contains the data specified on a case of a hard drive.

The table holds a lot of numbers and there seems no point in commenting them all — they are self explanatory. However, we have a comment to the table with results - the Samsung SP2004C hard disk supporting SATA II interface (its transfer rate is doubled to 3 Gbit/s) was also tested connected to Silicon Image SiI3124-2 controller that supports this new interface. The results are quite expectable — its power consumption remained the same from +12 V line and grew by 20-40 mA from +5 V line (compared to its connection to ICH5 SATA 1.5 Gbit/s) in data transfer modes (+40 mA in Read mode, +30 mA in Bus transfer mode, +20 mA in Seek mode). Thus, a faster interface (SATA II) will hardly provide real performance gain to your data storage system so far, but it will contribute to its heating (by 0.1-0.2 W).

But if you connect a SATA 1.0 hard disk with NCQ support to the SiI3124 controller (we carried out this experiment with Maxtor MaXLine III 7B250S0), in order to see whether NCQ support has an effect on power consumption of hard disks, you will see that the current remains the same in all the modes mentioned (we haven't evaluated possible average power savings due to a faster execution of same tasks). The only exception is Idle mode, when the current was much higher than in case of the ICH5 controller (720 mA versus 560 mA from +5 V and 440 mA versus 400 mA from +12 V) — in this case the SiI3124 host seemed not to be able to cooperate with the drive electronics (or vice versa?) in terms of using power saving modes during pauses between storage access.

A separate mention should be made of the fact that if we compare "identical" hard drives, equipped with different interfaces — Serial ATA and UltraATA — the serial interface turns out much more power consuming than the parallel one! Indeed, the interface difference costs Hitachi Deskstar 7K400 about 130 mA along the +5 V line (it's almost 0.7 W, dissipated by the hard disk controller alone!), Serial ATA expenses of the Maxtor MaXLine III 7B300S/R0 grow to 150 mA (nearly 0.8 W), Maxtor DiamondMax 10 6B200M/P0 - over 200 mA (more than one Watt!) Even in case of the "old" Maxtor DiamondMax Plus 9 6Y120M/P0 the difference of 100-120 mA does not seem that harmless. Samsung spends about 100 mA on SATA, Seagate Barracuda 7200.8 — average 150 mA (this figure varies from disk to disk). However, Seagate Barracuda 7200.7 Plus used to draw even more — 200-250 mA! Even WD Caviar SE drives, well known for their economical efficiency, draw about 120 mA from the +5 V line to support Serial ATA. The following diagram is more illustrative, it contains drive power consumption values from +5 V supply voltage (only) in host transfer mode (no access to platters). The drives are grouped here by series.

The conclusion is clear: if you are still sure that SATA drives are faster than their counterparts with parallel interface, be ready to provide an extra Watt (or even more, taking into account a host controller) per each SATA drive. :) It's a trifle in comparison with 100 W of a powerful processor, but if your system is more efficient and you try to make it maximum quiet by using every opportunity to reduce power consumption, the array of SATA drives is not for you. Even considering the general heat dissipation of such drives, SATA usage increases it by up to 10% or more!

Speaking of how the specifications stand to our measurements, the picture is rather odd. Some figures are similar, the others are noticeably different (it's more convenient to compare Table 1 with Table 3 below).

Speaking of the correlation between power consumption values specified on hard disks with real values measured in various modes - total dissonance! You can try and guess for yourselves what each manufacturer meant by these figures. :) For example, 5 V marked on a Hitachi drive is evidently lower than the voltage demonstrated in Seek, Read, and Write modes, while 12 V "covers" these operations with a safe margin and is lower only than the Start-Up current. 12 V in the new Maxtor drives covers even the real start-up current, but their 5 V is obviously lower than the real values for reading and writing. I can only assume that the values marked on some Seagate and Samsung drives correspond to the maximum current in Idle mode (that's rather far-fetched). But tell me please who needs these values? Power consumptions marked on most drives does not depend on the model (whether it's SATA or UATA). That's also wrong. To put it simply, you cannot trust the figures marked on hard disks. In fact they are useless and even harmful as they misinform users! :( Moreover, you cannot use them to judge about the real heat dissipation of storage devices!

Interesting conclusions can be drawn from the comparison of power consumptions of hard disks within the same series but with different number of platters. For example, the +12 V draw in Hitachi Travelstar has grown only by a quarter (disproportionate to the number of platters) from three (in the 7K250) to five platters (in the 7K400). But when the Maxtor DiamondMax 10 (UATA/133) has switched from 200GB to 300GB (2 and 3 platters), the power consumption has grown by 35% (almost proportional to the number of platters, but in this case we were surprised by a high spinup current in the SATA 6B200M0 model). What concerns Seagate Barracuda 7200.8, 400GB and 300GB models have almost the same current drain from +12V line (the power consumption of the 300GB model is a tad higher), while their younger sisters (200GB and 250GB models) consume less power by ~20%. Thus we can draw a conclusion that the 300GB model has three platters and the 250GB model - only two. By the way, the +12 V draw in the 2.5-inch SCSI Seagate Savvio 10K.1 turns out much lower not only in comparison with the Seagate Cheetah 10K.7, but also compared to all (!) modern desktop ATA hard disks.

What concerns power and heat saving in Quiet Seek mode (instead of regular Fast Seek mode), it shows only in active random seek mode (there is no difference in other modes) and concerns mostly the current on the +12 V line (lower current is used for "profile" positioning of brackets with heads). The power saving amounts to 3.2 W for Hitachi Deskstar 7K250, 2.8-2.9 W for modern Maxtor hard disks (and 2.4 W for two-platter DiamondMax Plus 9), about one Watt for Samsung SpinPoint P80 and P120 (their seek time actually changes very little), the same one Watt for WD3200JD/B and 2.5 W for WD2500JD/B from the previous series (with 80GB platters). It's up to you to decide whether the game is worth the candle, as this significant power saving (up to 3 W) will be noticeable only in specific tasks with active frequent seeks across the entire disk (like server loads), which suffer from slower seeks. However, considering that modern ATA disks practically don't lose any performance in Quiet Seek mode at the majority of typical "desktop" tasks (probably except for active swapping, if the system has insufficient memory), switching such hard disks to the Quiet Seek mode will do only good — they will become quieter and even a tad cooler. :) That's how I prefer using them.

Start-Up current

A separate mention should be made of the start-up current in hard disks. It keeps within 500-700 mA on the +5 V line (except for WD Raptor from the first generation with 930 mA and old Barracudas with 800-850 mA). But the main load certainly falls on the +12 V line, where peak currents (average for tenths of a second) reach 1.5-2 A. The easiest (towards a PSU at spinup) hard disks are Hitachi Deskstar 7K250/7K400, WD Caviar SE and RE (the +12 V start-up draw is below 1300 mA), as well as Seagate Barracuda 7200.7 Plus (about 1200 mA). However, all 7200.8 models from Maxtor of the last two generations also blend in with the list of "easy-going" hard disks with 1.3-1.4A start-up power. Samsung SpinPoint P80 and P120 (up to 1660 mA) and WD Raprot WD740GD/ WD360GD (about 1600 mA) are a tad worse in this respect, though even they look as good as pies in comparison with the voracious Seagate Barracuda 7200.8 (of all capacities and interfaces) requiring to draw 2.2-2.3 A from the +12 V line at start-up. I don't know why Seagate doubled the start-up current compared to its desktop models of the previous generations. But the sad fact remains - it is out of all notch compared to all the other modern desktop hard disks and even to high-performance SCSI hard disks from Seagate.

By the way, the latest Seagate 10K.7 and even 15K.4 SCSI hard disks would appear not so ugly in terms of start-up current: 1200 mA for one- or two-platter 10K.7 hard disks and just 1.6 A for the senior four-platter 15K.4 model — these are quite sparing parameters! It's quite easy to explain — the start-up current of Seagate SCSI hard disks is spread over quite a long period of time (they spin up for 10 seconds or more, when the start-up current is limited by electronics of a hard disk at a specified level), while most ATA models spin up much faster and their start-up current graph resembles a steep impulse with falling tilt rather than a long plateau. The hard disks on the next diagram are listed in the order of their maximum start-up power consumption.

Heat dissipation of the drives.

Current drains (especially on both power supply lines) are actually not very illustrative as far as heat dissipation is concerned. So we shall use them to calculate power consumption for each operating mode (see Table 3). Of course, the power in this case is calculated with regard to a voltage drop on the internal resistance of ammeters in power supply lines, that is it corresponds to this very case. The power may be slightly different with other voltages.

In addition to the above said about the increased SATA power consumption and possible power saving on Quiet Seek, we can note that the 2.5-inch SCSI Seagate Savvio 10K.1 demonstrates surprisingly low power consumption in Idle mode — bravo! The best 3.5-inch models in this respect are many WD Caviar SE hard disks and some ATA models from Maxtor, Seagate, Samsung, and Hitachi, as well as the Seagate SCSI Cheetah 10K.7.

Here is a list of hard disks in order of their power consumption and heat dissipation in active Seek mode:

And again ATA hard disks from Samsung and WD are a tad better than their competitors (by the way, the same picture was demonstrated by notebook models from these manufacturers, see our review). However, some Seagate models also look good, while Maxtor and Hitachi cannot boast of the economic seek mode. But you should keep in mind that they feature the highest power saving in Quiet Seek mode (within 3 W). So they have every prospect of success in the total leadership competition, their power consumption in this mode being reduced to 8-9 W!

It's also interesting that the WD Raptor WD740GD divides the list of hard disks in both categories (Idle and Seek) in equal halves. So this hard disk turned out not that power hungry and hot — even compared to many slower (less efficient) competitors.

In order to reduce the figures from Table 3 to common simpler and more useful denominator, we calculated two parameters, useful in practice: average power consumption of hard disks during typical user operations and during intensive (constant) HDD operations. To calculate these benchmark characteristics, which actually do not claim to be some indisputable truth, I used two typical usage models of hard disks:

1. Model of the average hard disk power consumption for typical unhurried operations of a user (for example, office work or editing graphics) can be described by the following formula:

P typ =( Idle *90%+ Write *2.5%+ Read *7.5%)/100%,

where lettered modes denote the power consumption of a drive from both voltage sources in the corresponding modes; digits (multipliers for these power values) denote percentage of the HDD mode duration (we take maximum power consumption values for reading and writing, which correspond to the beginning zones of a disk; Seek mode is actually metered here through reading and writing). This model is based on the assumption that read/write HDD operations make up 10% of the total time for the typical desktop usage.

2. The average power consumption during intensive hard disk operations (for example, defragmenting disks, scanning the surface, copying files, checking files for viruses in the background, etc) can be defined by the following formula:

P max =(Write + Seek + Read *3)/5

Calculated power consumptions are used to plot the following diagrams.

These results are evidently close to the alignment of forces in the Idle mode — the most economic hard drives consume just 5-6W in this mode, the coolest hard disks are WD Caviar SE and Samsung SpinPoint, though some models from other manufacturers are also very economic. Theoretically, the gap between the winners (if we don't take into account Savvio and Cheetah 15K.4) and "the losers" is not that large here — 6 W and 8.5 W. Power consumption of the majority of ATA hard disks is about 7 W ± 0.8 W. That's why the difference in operating temperatures under the same cooling conditions will be just a couple of degrees. We can also note that the largest power consumption is demonstrated by ATA hard disks from Maxtor and Seagate of the previous generations, that is the efficiency of the latest generation is obviously better.

The mean power consumption of hard disks under intensive (constant) load is shown below:

Again you can see that WD Caviar and Samsung ATA hard disks are noticeably "cooler" than those from other manufacturers, even the WD Raptor WD740GD has gone up to the middle of the list! Hard disks from Seagate, Maxtor, and Hitachi are generally "hotter" by a couple of Watts, though much depends on a given model and you may find economic models even among them. Heat dissipation of ATA hard disks under intensive load keeps within 7.5-12 W, the average value is about 10 W. That's what power you should keep in mind when you choose a cooling system for single hard disks inside a PC case. Theoretically, this data agrees well with the read/write/seek power consumptions published in the specifications.

Conclusion

In fact, all main conclusions from our experiments on measuring power consumption and heat dissipation of modern 3.5-inch hard drives have already been drawn in the body of the article, so we can only add the following:

1. Measuring power consumption is a convenient and powerful tool to evaluate heat dissipation of hard drives in various operating modes, which can provide an attentive experimentalist with a lot of additional useful information.

2. Regard temperature evaluations of HDD heat dissipation (and operating temperature conditions) with great care. You shouldn't decide whether to install an active or passive HDD cooling system relying on other people's temperature measurements (no matter how competent they are) of a given model or series, you can trust only your personal experiments with your sample installed in your system environment.

3. Specifications on power consumption of a hard disk or, moreover, this data printed on an HDD case should be taken critically. They will seldom give you an idea of the true power consumption and heat dissipation of hard disks! You'd better trust the reality perceived through your senses.

4. Heat dissipation of desktop hard disks has been steadily going down of late, though the appearance of fashionable serial interfaces (SATA 1.0 and SATA II) obviously does not make for it. At the same time, Quiet Seek mode can sometimes reduce heat dissipation of a hard disk much lower than it is increased by using the SATA interface.

5. In some cases you should pay special attention to providing proper load that does not exceed PSU capacities, when hard disks spin up — it even concerns some modern ATA models, especially hard disk arrays.

6. Some modern high-performance SCSI hard disks are very mild in terms of heat dissipation, they can even compete with desktop ATA models and sometimes can operate only with passive cooling. Seagate Savvio 10K.1 turned out the most economic model among the high performance hard disks, having outperformed even all 3.5-inch ATA hard disks!

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