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Micron Blog

Part 5: Limitations of the HDD

An HDD's Mechanical Limitations

  1. Tape Drives
  2. Magnetic Drum Memory
  3. The Birth of the Hard Drive
  4. The 5.25-inch Hard Drive
  5. Limitations of the HDD
  6. The RAM SSD & NAND
  7. NAND in SSDs

In spite of new technologies like perpendicularly aligned bits and HAMR, HDDs are mechanical devices at heart and, as such, they face many performance challenges. Indications are that, ultimately, as storage systems continue to evolve, HDDs will be replaced.

Mechanical devices cannot improve as quickly as solid state technologies can. For example, "over the past 20 years, microprocessor technology—which plays a key role in data storage efficiency and function—has enabled CPU performance to nearly double every 18 months. Put another way, CPU performance has increased 16,800 times between 1988 and 2008, but HDD performance has increased by just 11 times." [37]

Figure 7: Relative Performance Improvement for CPUs and HDDs

Even leading HDD manufacturers recognize the HDD performance problem. When Seagate Technology introduced faster, 15,000-RPM disk drives in 2004, it released a white paper describing the need for better HDD performance.

"Dramatic advances in processor speed, RAM size and RAM speed have combined to accelerate system performance to levels unthinkable just a few years ago. Such powerful hardware resources have made feasible software solutions with increasingly sophisticated and comprehensive capabilities, enabling business productivity to climb at a remarkable rate. Yet one aspect of system evolution has historically lagged behind: disc drive performance. While impressive advances in density have yielded exponential growth in disc drive capacity, disc drive speed has achieved only modest gains over the years," [38] Seagate said.

Figure 8: HDD Performance has not kept pace with other System Components [3]

To try to close the HDD performance gap, manufacturers have increased the drive’s rotational speed, added more advanced heads, and used techniques like short stroking, which restricts data to 5%–30% of the platter to boost performance. Western Digital, for example, recently released a speedy 20,000 RPM HDD. But faster and faster disk rotation cannot be a lasting answer because these high-speed HDDs potentially make more noise, devour more power, and become increasingly less reliable. In addition, these higher-performance HDDs all sacrifice capacity. Each time the CPU issues a command "the hard drive’s mechanical system must then seek the requested data block or file by rotating its spinning platter and reaching out with its actuator." [39]

To be sure, HDD engineers have continued to improve these devices and thus, stave off their ultimate extinction.

HDD Mean Time Between Failures (MTBT)

"It is estimated that over 90% of all new information produced in the world is being stored on magnetic media, most of it on hard disk drives. Despite their importance, there is relatively little published work on the failure patterns of disk drives and the key factors that affect their lifetime. Most available data are either based on extrapolation from accelerated aging experiments or from relatively modest-sized field studies. Moreover, larger population studies rarely have the infrastructure in place to collect health signals from components in operation, which is critical information for detailed failure analysis." [40]

This seeming lack of information about a modern HDD's mean time between failures is a problem for large data centers and for the potential survival of HDDs. To try and shed light on the subject, Google created the first, large population HDD failure study in 2006 and released their findings at the 5th USENIX Conference on File and Storage Technologies in February 2007.

The Google research categorized dozens of failure types, found a handful of unexplained relationships, and generally showed that HDDs fail more often than manufacturers predict [41].  The study was an important first step since it provided users with foundational data for further research and it gave HDD manufacturers a sort of failure map. Solving some of these issues may result in better HDDs in the near future. If they go unaddressed, however, these failure issues could spell the end of HDDs.

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Notes: [37] Justin Sykes, "Performance Productivity for Enterprise Applications," Micron Technology, Inc., Boise, Idaho, (July 30, 2008): page 1, downloaded from http://download.micron.com/pdf/whitepapers/performance_productivity_for_ent_apps.pdf. [38] “Economies of Capacity and Speed: Choosing the most cost-effective disk drive size and RPM to meet IT requirements,” Seagate Technology LLC, Scotts Valley, CA, (May 2004): page 2, downloaded from http://www.seagate.com/docs/pdf/whitepaper/economies_capacity_spd_tp.pdf [39] Sykes, "Performance Productivity for Enterprise Applications," page 2. [40] Eduardo Pinheiro, Wolf-Dietrich Weber, and Luiz Andre Barroso, "Failure Trends in a Large Disk Drive Population," Google Inc., Mountain View, Calif. (February 2007): page 1. [41] Pinheriro et al, page 12.

About Our Blogger

Dean Klein

Dean Klein is Vice President of Memory System Development at Micron Technology. Mr. Klein joined Micron in January 1999, after having held several leadership positions at Micron Electronics, Inc., including Executive Vice President of Product Development and Chief Technical Officer. He also co-founded and served as President of PC Tech, Inc., previously a wholly-owned subsidiary of Micron Electronics, Inc., from its inception in 1984. Mr. Klein’s current responsibilities as Vice President of Memory System Development focus on developing memory technologies and capabilities.

Mr. Klein earned a Bachelor of Science degree in electrical engineering and a Master of Electrical Engineering from the University of Minnesota, and he holds over 220 patents in the areas of computer architecture and electrical engineering. He has a passion for math and science education and is a mentor to the FIRST Robotics team (www.USFIRST.org) in the Meridian, Idaho school district.

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