Storage technologies—the long view

Computer Technology Review, July, 2003 by Fred Moore

For vendors and end-users alike, the progress of technology marks a never-ending process to successfully store, retrieve, migrate and effectively manage the entire data life-cycle process. We have extensively focused on the management challenges in trade journals, conferences and the media in the past few years, recognizing that the biggest storage challenge is its management. In order to better understand how we are preparing our storage infrastructure for our future, we must take some time to look ahead and see just what it is that we may likely be managing.

Disk Futures Roadmap

As of mid-2003, just a few significant disk drive suppliers remain: Seagate, Maxtor, Western Digital, IBM, Fujitsu, Samsung, Toshiba, NEC and Hitachi. With Hitachi's purchase of IBM's disk drive business, the majority of the world's disk drive producers is now Asian based, although the majority of disk drives are still produced by North American-based companies Seagate, Maxtor and Western Digital.

Magnetic mass storage technology advances have enabled the migration of disk units to 3.5-inch and smaller diameter form factors. The 3.5-inch and 2.5-inch form factors are present in all segments of the market: server, desktop, and mobile. The recent introduction of a 1-inch form factor may point the way to future configurations of the disk drives though these presently remain confined to the entertainment sector of the storage industry. There are many signs that 2.5-inch form factor disk drives will soon start to displace 3.5-inch drives as the de-facto standard due to the increases in areal recording density.

Magnetic disk areal density has grown at an impressive 60% compound annual growth rate historically and has accelerated to greater than a 60% rate since 1999. It is likely that the rate of disk areal density increase in magnetic recording will start to drop below 100% annually due to the greater difficulty in making the new technology work. A particular technical challenge will be making magnetic recording heads with track width dimensions that are smaller than the minimum feature size of the optical lithographic equipment used in the semiconductor industry. From a usage perspective, the access density of increasingly higher capacity disks has become a mounting performance concern even though the price per megabyte steadily declines. Over the next five years, the likelihood of perpendicular recording using a patterned media may appear to further increase capacities. Perpendicular recording enables the bits to be magnetized on end, perpendicular to the disk surface (rather than parallel to the surface). This greatly improves recording density and the raw drive data rate. Thermo-mechanical data writing on plastic substrates continues to achieve positive results and may bypass the anticipated super-paramagnetic limit completely.

Tape Futures Roadmap

Although somewhat less form factor driven than disk, tape drives are also physically shrinking; many drive product offerings are now in the 5.25 -inch and 3.5-inch form factors. Most formats have settled on the 5.25-inch cartridge. The very low-end (single-user systems) of the tape market continues to shrink in the face of small form-factor removable disks. In the middle markets and enterprise sectors, automated tape libraries have become commonplace and range in capacity from tens to thousands of tapes, with total capacities now exceeding I petabyte (1PB = 1015 bytes) per library. Tape cartridge roadmaps identify native capacities up to 8 terabytes and drive data rates up to 800 megabytes per second.

Magnetic tape continues to offer the highest probability of success in achieving the maximum total volumetric density and maximum data rate combined with the lowest cost per megabyte of any technology. The simplified use of tape has made tape accepted in a wide variety of data storage applications and tape is no longer only positioned as a backup/recovery technology. In the interactive storage environment, this problem is largely overcome through the use of embedded disk buffers used as a cache for the tape library. The largest growth area for magnetic systems is in long-term data retention and archival storage. Government regulations and numerous other legal issues are now mandating that certain types of data be retained in a machine readable format forever.

The majority of today's tape systems use linear recorded tape. Helical scan magnetic tape systems, developed and produced by Pacific Rim manufacturers and led by Sony. have made significant inroads into the tape market over the last few years and totally dominate the digital video recorders markets. Linear tape cartridges have begun to mirror the >60% annual areal density growth rate of magnetic disk systems over the last decade through two key breakthroughs. These are the incorporation of magneto-resistive heads and track following servos. Five years ago, several tape cartridges were needed to backup a single disk drive; today, a single tape cartridge can backup any disk drive. These two technologies have allowed linear tape systems to approach the areal density capabilities of helical scan magnetic tape systems. Challenging aspects of maintaining this growth relative to magnetic disk are the twin requirements of media interchangeability and backward compatibility

Optical Storage Futures