Being one of the few remaining mechanical components of the computer system, the hard disk drive is also one of the major power consumers. A spinning hard disk platter effectively turns power into heat, working contrary to user expectation. Not surprisingly, most hard disk drive manufacturers have implemented a number of power saving features, reducing the impact of disk drives on one’s electric bill. But one power saving feature from Western Digital has come under increasing fire: the Intellipark system found in their Caviar Green hard disk drives is a serious liability when used in many “always-on” scenarios.
The Green Revolution
Western Digital’s Caviar Green series of hard disk drives is part of a trend in the hard disk industry toward power saving drive technologies. The Caviar Green series uses half the power of conventional desktop hard drives through intelligent power management and reduced spindle speed.
For more about these drives, see “What Is The Secret To Efficient Hard Disk Drives?“
Although marketed as providing nearly the performance of full power drives, the Caviar Green series really is substantially slower when pushed to the limit with random reads and writes. Happily, most users never really exercised their hard disk drives, and would see very little performance difference and a great deal of power savings by going with the Caviar Green or competing models from Seagate or Samsung.
One of the basic tricks Western Digital employees with the Caviar Green series is reduced spindle speed. Conventional desktop hard drives typically spin at 5400 or 7200 revolutions per minute. While Western Digital does not officially share the spindle speed of the Caviar Green series, independent tests have shown it to be only slightly more than 5400 RPM in some drives and as high as 6000 RPM in others. Contrary to early published reports, spindle speed is fixed rather than variable. In contrast, Seagate’s Low Power series spins at 5900 RPM, while Samsung’s EcoGreen uses a conventional 5400 RPM speed.
In order to attain good performance, all three vendors use the highest density platters available. Packing the bits close together accelerates throughput for sequential operations, making the drives appear to be as quick as one with a faster spindle speed. They also loaded the drives up with RAM cache: 64 MB in the case of the Western Digital Caviar Green series. This also helps accelerate performance, especially in random I/O situations.
IntelliPower and IntelliPark
IntelliPower is Western Digital’s trade name for a variety of power saving technologies, but reduced spindle speed is the centerpiece. But there is more to IntelliPower than spindle speed: Western Digital also ups the cache and includes power saving features to reduce the load on the disk drive.
One of the more unusual features of these drives is IntelliPark, which positions the read/write heads unloaded in a parking position and turns off certain drive electronics. From the factory, IntelliPark is quite aggressive, adopting this mode (referred to as “idle 3” by the company) after just 8 seconds of non-use.
The Problem with IntelliPark
This is no problem for operating systems like Microsoft Windows, which have been tuned to leave disk drives in the idle state for as long as possible. But Linux and RAID devices are not nearly as friendly. Assuming that hard disk drives are always spinning, many of these systems write data much more frequently, often every 10 to 20 seconds.
When Western Digital Caviar Green drives are used in systems that write data very frequently, IntelliPark can become a serious liability. Continually parking and on parking the heads causes wear and tear, potentially leading to drive failure. The difference between a park operation every 10 seconds and one every 5 minutes is dramatic, both in terms of drive longevity and power savings.
Enthusiasts have been quick to suggest that this feature is a critical design flaw, causing otherwise good hard disk drives to fail. Predictably, Western Digital sees things differently. They contend that the Caviar Green series was designed to be used in operating systems like Microsoft Windows, and suggest using other drive models in Linux and RAID systems. They also offer an idle mode update utility which allows end-users to tune this parameter or turn it off entirely.
Although I cannot agree with the enthusiasts claiming that Western Digital Caviar Green hard disk drives are defective or fatally flawed, the execution of the IntelliPark feature are debatable. Parking heads every 8 seconds seems overly-aggressive to me, especially since many operating systems are not optimized for this condition. I continue to recommend using RAID optimized drives in RAID systems, but it seems that Linux desktops ought to be able to use desktop drives like the Caviar Green.
I applaud Western Digital for creating and distributing an idle mode update utility, since it allows these drives to be used in nearly any operating system while sacrificing only a little bit of the power saving benefits. My own experimentation shows that these drives function just fine in my Drobo storage array without excessive load/unload operations, so I continue to recommend them. Users should beware of these drives in devices such as this, however, and should consider using the idle mode update utility to disable IntelliPark.
Perhaps Western Digital should update the firmware of these drives to detect excessively frequent load/unload operations and automatically disable IntelliPark in these cases. Although they are within their rights to design a drive that is applicable only to certain use cases, automating this tuning would save them from unnecessary PR backlash.