Is it tape and disk or tape versus disk?

It's absolutely incredible! The cost of storing a terabyte of data today costs about 1/1000th of what it cost just 11 years ago. It wasn't very long ago that everyone measured the cost of storage by dollars-permegabyte. Today it's dollars-per-gigabyte, and there are already some references to dollars-per-terabyte. We've also gone from data transfer performance measured in KB/sec to MB/sec to GB/sec in the past decade.

Every indication points to the promise of continued improvements in the cost and performance of storage, depending on the technology involved. But for the most part, the relative cost of these technologies to each other has, and will remain, fairly constant.

High-end, enterprise-class disk drives, typically defined as having fast SCSI or Fibre Channel interfaces, occupy the top tier of the pricing structure (see Table). These drives are almost always configured in large, complex arrays that provide various levels of data protection, such as RAID-5 mirroring and redundant power supplies.

"Performance disk drives," as categorized by IDC and other analysts, first hit the market around 1998. These drives have EIDE, ATA and now SATA interfaces and provide much better value than their predecessors, but with lesser performance and reliability as compared to their enterprise-class cousins. Performance disks are usually configured in simple RAID arrays or as Just a Bunch of Disks (JBOD) to provide basic data storage and access.

Optical disk technology had its beginnings in the mid-1980s, but has been dominated by Magneto-Optic products since 1996. MO stayed comfortably in the middle tier of the storage pyramid until 2000, when its price per GB was matched by the performance hard disks and then overtaken in 2001. But the king of cost-effective storage has always been magnetic tape technology, and given the product roadmaps published by major tape manufacturers and members of the Tape Technology Council, this trend will continue.

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Cost of Ownership

Comparing the Total Cost of Ownership (TCO) between any two storage solutions is very complicated, due to the number of variables. For example, the cost of the tape library robotics is spread across the number of tapes slots in the tape library, and this can vary from 7 to over 10,000 slots. Therefore, to keep this as simple and effective as possible, the price points in the Table show what it costs to add incremental capacity after a storage system is already in place.

No Limits in Sight

The dramatic decrease in the cost of storage, across the board, has been somewhat enabled by improved manufacturing processes and the use of smaller, less expensive components. But the vast majority of savings has been due to the research and engineering that has allowed ever-increasing capacity to be stored on a given recording surface, such as the hard disk platter in a 5.25-inch drive.

As the capacity of hard disk drives has increased over the years, the capacity of tape cartridges has kept pace. In 2002, the INSIC (Information Storage Industry Consortium) reported that over the previous 8 years, tape technologies had maintained a constant ratio of 3.33 times the capacity over a single disk drive platter, and predicted that this ratio would remain unchanged at least through 2008.

For years, scientists have been forecasting that the next generation of disk drives will reach the theoretical limits of areal density (the number of bits that can be stored on a square inch), but they have been able to increase the areal density onto the disk and adjust their understanding of physics in the process. It remains a possibility that at some point they will reach their limit, but by then there should be some new way of storing data--perhaps using nanotechnology.

In contrast, there haven't been any predictions about how much information can ultimately be stored on a magnetic tape. Each of the major tape drive and media manufacturers has already proven the science behind at least the next two generations of capacity-doubling product releases, and sees no limits in sight. And tape also has the advantage of being able to add even more capacity by lengthening the tape. This is done by creating substrate materials that are thinner than the previous generation, thereby allowing more tape to be fit into the existing cartridge. The size of a disk platter cannot be increased in this manner, so tape engineers have an advantage in the ongoing capacity-increases and cost-cutting wars.

Storage by Application

In the enterprise, it is common practice to store the data from critical business applications such as CRM, ECM, EDM, ERM, ERP, OLTP, RPM, SRM, etc., on high-end disk systems. (And who knew that the software industry had more acronyms than the storage industry?) Files from office applications are typically stored on the more value-priced performance disk systems, while archive data that needs to be readily accessible often finds its way to optical media. Tape has been used for backing up everything that's on disk plus provides disaster recovery ability, and is also used for long-term archival.

If the pricing points shown in the Table were plotted on a linear chart, one could come to the conclusion that the costs of all these technologies are quickly converging toward $0. This probably explains why some hard disk vendors are trying to expand their wares beyond their traditional applications. But if the price points are plotted on a log chart (Figure), the storage pricing trends become much clearer. Rather than compressing on each other, they are mostly remaining parallel to each other.

Something to Think About

It may be tempting to think that the price/GB for performance disk is now not that much more than for tape, and therefore decreasing disk prices will lead to the near-term obsolescence of tape. But when we start thinking in terms of terabytes, a disk price of $1,500/TB vs. a tape cost of $350/TB does not really seem so competitive. Before looking at the simple cost of a single disk or tape, make sure that you consider the entire size of your data to be processed, backed up, and archived.

Even if the scientists working on cramming more bits onto a disk surface can continue to overcome their latest understanding of theoretical areal density limits, it will still be a number of years before even value-priced disk systems can compete on price with tape. And further, disk may never reach the portability, reliability and security of tape storage. So, it's definitely not tape versus disk but rather tape and disk. Without tape, your data is at risk!

The best example of storage types crossing the application line is the recent release of several disk-to-disk backup solutions, where a disk subsystem is configured to emulate an automated tape library. The thinking is that with SATA disk drive prices approaching the price points of tape, customers will pay the premium to achieve the faster performance afforded by disk. But of course, the performance benefit is only applicable to data recovery, since today's tape drives can record data faster than the primary disk can send it. And a disk-based backup solution does not provide the ability to physically remove the data and move it to an off-site vault for disaster recovery purposes. Therefore, most companies that employ a disk-based backup system will also use a tape library to off-load the data after it's been backed up or pay to mirror the data to another storage system in a secondary data center. In essence, the cost of the disk-to-disk solution is attributable solely to the increased performance for data retrievals and does not replace any of the costs or the reliability associated with a traditional tape backup solution.

Table: Comparison of Price Per Gigabyte (US$/GB)

  Year        1994      1996      1998     2000     2002    2004
  Tape
  Media          $5.00     $3.00    $1.80    $1.00   $0.60  $0.35
Commercial
  Optical
  Media         $80.00    $40.00   $25.00   $15.00   $7.50  $2.00
Performance
  Hard Disk      N/A       N/A     $80.00   $11.00   $4.50  $1.50
  Enterprise
  Hard Disk   $8000     $1200     $400.00  $100.00  $25.00  $8.00

Source: Creative Businesses, Inc., February 2004.

www.tapecouncil.org

Richard Harada is president of the Tape Technology Council, the primary industry resource for promoting, integrating and using tape storage devices. A non-profit organization comprised of leading tape storage companies, functioning as a conduit for information exchange between manufacturers and the industry. TTC members include Fujifilm. IBM, Imation, Maxell, Quantum, Sony Electronics, StorageTek and TDK.