HDD Units (posted after sent by Jim)

Happy 50th, hard drive. But will you make it to 60?

Threatening HDD, flash memory will soon be available in 64GB capacities -- with larger devices coming

September 26, 2006 (Computerworld) -- After 50 years, the useful life of the hard disk drive (HDD) is increasingly being threatened by SDRAM and flash-based semiconductor solid state disk (SSD) storage. For example, Samsung Electronics Company Ltd. has announced plans to release a 64GB solid state disk drive in a 2.5-in. form factor with an IDE/ATA or Serial ATA interface. And current 32GB flash memory is selling for $1,800 or less. So the questions are, Is SSD ready to surpass HDD in capacity and price? And, Has the HDD reached the physical limits or can the technology be pushed further?

Over its 50-year life span, the HDD has evolved from a 5MB storage device with 50 24-in. disk platters about the size of a household refrigerator to a 1-in. 8GB device found in Apple iPod and other MP3 players. Physically larger than the 1-in. HDDs found in consumer MP3 players and cell phones, 7,200-rpm, 3.5-in. HDDs have capacities of 750GB priced in the $400-to-$500 range with even larger 1TB HDDs just around the corner. For a good HDD synopsis and history, check out the recent Computerworld piece "From Elvis' hips to spinning disk: 50 years of innovation."
 

Figure 1 Relative HDD trends and directions (Click image to see larger view)

To remain viable as a storage technology, HDDs must continue to improve on price, reliability, durability, power consumption, footprint, capacity and performance (see Figure 1). Perpendicular recording technology that is replacing longitudinal recording on HDD combined with other enhancements should extend the useful life of the HDD for about another 14 to 15 years. Researchers like Mark Kryder, chief technology officer of Seagate Technology, estimate that perpendicular recording combined with other technology enhancements should enable the HDD to evolve out to around 2020.

At some point before then, a major technology shift or revolution will be required unless a significant breakthrough in physics and material composition among others can extend the HDD even further. What this means is that since it takes about five years for a technology to be fully integrated into an ecosystem like the storage industry, to be available around 2020 would need to understand what the replacement technology will be sometime around 2015 or so. While 2015 is less than nine years away, that still leaves plenty of time before you will need to unplug your existing storage systems.

Storage technologies or disk systems traditionally have been replaced on three-to-five-year cycles that should enable users to deploy several more iterations and generations of HDD-based storage before some new technology is defined and developed and products are ready for mission-critical deployment. We should start seeing signs of a new major technology shift in about nine to 10 years. However, between now and then, assume that we will continue to see many smaller (on a relative scale) technology improvements and evolutionary enhancements appear.

Perpendicular recording (Figure 2) is currently being deployed by major HDD manufactures across their product lines. Using perpendicular recording, more data can be stored in the same form factor (higher density), enabling reduction in number of platters required while increasing capacity, compared to longitudinal recording. There are more improvements in the works for the disk drive, including, better reliability, less power consumption, smaller footprints, continued drop in price per GB and, of course, increased capacity.

Figure 2: Longitudinal and perpendicular recording Source: www.seagate.com

A challenge to building larger-capacity and smaller HDDs is the barrier known as super paramagnetic phenomenon. Super paramagnetism occurs when the magnetic particles on an HDD platter become so small that the magnetic energy holding the particles in place representing a bit can be influenced by thermal energy, resulting in lack of data integrity. The traditional approach for recording bits of data on a HDD using longitudinal recording was heading for the super paramagnetic brick wall limiting future HDD growth without having to increase the physical size of a disk drive.

To delay the effects of the super paramagnetic barrier for several years, perpendicular recording is being adopted by major HDD manufactures. For example, in mid-September 2006, Seagate demonstrated a record ariel density of 421G/bit per square inch that should result in future disk drives of 40GB or more for 1-in. and 275GB for 1.8-in. consumer electronics products.

At 421G/bit per square inch, future 2.5-in. HDD (6.25 square inch per platter surface) about two to three years away for notebooks and new generation of enterprise-class 2.5-in. disks should have capacities pof about 500GB. For 3.5-in. HDD manufacturers like Hitachi estimate that we should be seeing 2TB HDD around 2009 or 2010 with 1TB 3.5-in. HDD just around the corner. Smaller consumer HDD improvements for 1.8-in. HDD should have capacities of around 200GB in a couple of years. To put this into perspective, an Apple iPod or other MP3 player could for example have more storage than a typical currently shipping laptop or desktop computer.

To enable the HDD to get out to the 2020 timeframe, perpendicular recording will need to be combined with other types of technology including smaller form factor drives. For example new technology being worked on in R&D labs include heat-assisted magnetic recording nick named (HAMR) or thermal assisted recording (TAR) or bit pattern media are seen as possible technology to be combined with others to continue the HDD evolution until around 2020.

A possible threat to the HDD in I/O-intensive and time-sensitive applications, rugged and harsh environments, and portable devices including notebook computers is SDRAM or flash SSD. The primary advantages of SSD is that there are no moving parts, so seek times are dramatically decreased to improve performance and power consumption compared to a traditional HDD. SSD in the form of SDRAM (RAM) has been around for several decades as a high-performance storage solution for I/O and transaction intensive applications. SSD has been limited in capacity due to high cost of RAM compared to HDD storage, but similar to the HDD, SSD capacities continue to increase while prices decline. Today there are two primary types of SSD technologies one being RAM similar to what you would find in a typical server or cache in a storage device that requires power to preserve contents of memory and the other being NAND based flash.

Flash, also known as a disk on module (DOM), is most commonly found in portable media players and USB flash drives. Unlike SDRAM, it does not require power to preserve memory contents eliminating the need for battery and alternate power sources. While flash memory may not be as fast as high-speed RAM, it has an advantage in that it is available in large capacities at relative lower prices with improvements in both occurring on an annual basis. Vendors, including Samsung, are deploying flash-based SSDs with ATA and Serial ATA interfaces in 2.5-in. form factors for use in harsh environments and notebook computers to support faster boot and restore times while drawing less power than HDDs.

SSDs are available or soon to be available in capacities up to 64GB with larger devices on the drawing board. For example an IDE/ATA or SATA 32GB NAND based flash drive sells for about $1,800 (or less) with prices continuing to decline. By comparison a 3.5-inch SATA 7,200RPM 750GB HDD sells for about $400-500 USD. High capacity (multiple gigabyte ) SDRAM based SSD devices are also available from vendors including Texas Memory Systems.

There is a caveat with NAND flash based technologies in that they are not optimum for continuous reuse and re-cycling compared to RAM and HDDs. This has led to the development of hybrid disk drives that combine a HDD with large amount of flash and RAM to enable the HDD to spin down and I/Os resolved from RAM and flash until the HDD is needed. For example the Seagate Momentus PSD (power saving device) that combines a traditional 2.5-in., 5,400-rpm 160GB notebook HDD, 256MB of flash and 8MB of RAM cache. Another example of a hybrid HDD is the Samsung flashon (Figure-3).

Figure 3:
Samsung hybrid HDD (flashon)
Source: www.samsung.com

As the industry has seen in the past, combinations of different technologies can be expected to appear in storage systems and servers to help address data storage and I/O performance needs. For example some vendors may incorporate multiple gigabytes of flash as an embedded SSD on server motherboards to complement existing HDDs. Storage vendors may incorporate larger amounts of SDRAM and flash as tiered cache in front of larger quantities of high capacity 2.5-in. and 3.5-in. enterprise and desktop drives for tiered storage.

Some general trends include:

·                                 Continued decline in pricing while capacities increase for HDD and SSD technologies

·                                 Larger capacities, smaller footprints, less power consumption, better performance

·                                 Better reliability and durability with higher MBTF (some disks have 5+ year warranties)

·                                 Hybrid technologies combing HDD, SDRAM and flash as an integrated device

What happens around 2020 is still not clear, and there is plenty of time for new technologies to evolve -- some perhaps even revolutionary. There could be new breakthroughs in material compositions and recoding techniques to further extend HDD usefulness while semiconductor capacities increase and prices continue to decrease. Perhaps holographic storage that we have heard about for the past 10 years or so may finally be ready and economically viable for production sometime in the next 10-20 years. It's fairly safe to say that the death of the HDD after 50 years is still greatly exaggerated, so keep an eye on emerging data storage technologies to support storing larger amounts of data in more locations for longer periods of time.

HDD RAM/SDRAM NAN FLASH Benefits Reliable proven technology with good economics, capacity along with diverse packaging options Low power requirement, higher performance for server boot times and improve OLTP and other I/O intensive applications Improved cost vs. RAM, good performance and no need for battery to preserve data when is power lost Caveats More power, sensitive to shock, vibration and less performance compared to SSD Expensive vs. HDD and flash. Battery needed to preserve data during loss of power Similar to SDRAM along with limited reuse cycles compared to SDRAM and HDD technologies Use for Price-sensitive applications that require large amounts of storage with good performance I/O and time-sensitive applications including OLTP or where power consumption and durability are concerns Portable storage and media players, consumer products, tiered cache, appearing in hybrid HDD-based devices