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Sense and sensibility about tape and disk

Posted on May 01, 2008

By David G. Hill

The rise of disk–based backup–and–restore technologies, most notably virtual tape libraries (VTLs), has been well–documented. That is likely to continue for the foreseeable future, which raises a key question: What is the impact of this trend upon traditional tape storage technologies?

One school of thought (and one that is encouraged by some vendors of disk–based data–protection technologies) is that there is no longer a need for tape. That viewpoint is reinforced by the fact that some businesses have eliminated tape technologies from their storage infrastructures.

A second school of thought suggests that while disk–based data–protection technologies will continue to prosper, tape technologies will continue to play a complementary role with disk.

A recent study of tape and disk technology buyer perceptions, conducted by Fleishman–Hillard Research for the Linear Tape Open (LTO) Program—Hewlett–Packard, IBM, and Quantum—favors the second school of thought. The research was conducted across a broad range of vertical markets, and the majority of the respondents (83%) were systems/network administrators.

The results were interesting. Nearly three–quarters (70%) of companies use a combination of tape plus disk for interim (as opposed to long–term archiving) data backup purposes, and nearly three–fifths (58%) use both tape and disk for long–term archiving (see figure). Surprisingly, nearly three–fifths (58%) of current disk–only users plan to start using tape for interim storage. In fact, the use of disk–only systems decreased by 13% in the past year. In addition, of those companies that are currently using both disk and tape for interim storage, more than half (52%) say they planned to increase tape usage within their combined systems.


On the long–term archiving front, 22% of current tape–only users plan to increase tape usage and 52% plan to maintain current usage. Of current disk–only users, 68% plan to begin using tape for long–term archiving. Meanwhile, 51% of those that currently use combined tape–plus–disk systems plan to increase tape usage for long–term archiving.

To paraphrase Mark Twain, reports of the death of tape have been greatly exaggerated. Why is that? What should be the relationship between the use of tape and disk for data protection? Before we can answer those questions, let’s consider how many distinct physical copies of each piece of data need to be available.

The answer is a minimum of four copies—the production “original” and three data–protection copies. The local site holds the production copy and one data–protection copy, while two data–protection copies should reside at a remote disaster–recovery site. If either the local or remote site goes down, two copies of the data are lost (at least temporarily). Bottom line: You always need a spare copy if anything should happen to the production copy.

Where do VTLs fit in to this? Note that a VTL using data de–duplication has only one physical (as well as logical) copy of the data. While the VTL may be highly efficient in storing data compared to numerous copies of tape, it still houses only that single copy. If the disk array that supports the copy is corrupted or destroyed, the data is lost. To avoid being left without any data protection, additional physical copies are necessary. Of course, those other copies could be on disk, but should they be? The first battleground is economic. There are many dueling cost analyses examining the TCO of tape versus disk. For example, the LTO Program has an interesting cost–analysis white paper on its Website.

But the validity of those cost equations depends on the assumptions made. One simple part of the equation typically finds that tape media is less expensive than an equivalent capacity of hard disks. But if tape media are used inefficiently to make many unnecessarily redundant copies, then a single disk using data de–duplication may be more cost–effective.

The second battleground is simply logic. Cost—although important—should not be the only determinant. Pure tape is not likely to be an effective solution for most companies, so the question comes down to disk–only solutions versus a blend of disk and tape for backup/restore data protection.

There are some advantages to having tape as part of the mix. An offline tape is as “green” as it gets (since no power or cooling is required for tapes that are offline), which should be factored into a TCO analysis. There may be a limit to the overall power and cooling that a data center can use, and that constraint is typically not part of a TCO analysis.

Next, offline tape is essentially secure from network attacks, which is one benefit of having a second technology for data protection in place. You don’t want to have all of your backup/restore processes relying on the same technology in case a systematic problem, such as data corruption due to a software bug, affects that one technology.

All in all, the research study suggests LTO tape is likely to play a continuing or growing complementary role in backup–and–restore operations, along with disk. That does not mean that businesses will not think about how to use their tape technology investment more efficiently. For most IT shops, however, a blend of disk and tape appears to be the strategy of choice for the foreseeable future. ¿

David G. Hill is a principal with the Mesabi Group research and consulting firm (www.mesabigroup.com).


Tracking tape media shipments/revenues

Revenues from backup tape cartridges topped $351 million in the fourth quarter (the most recent period for which data is available), according to the Santa Clara Consulting Group’s quarterly Backup Tape Tracker report. LTO cartridges accounted for a large portion of overall revenues—more than $262 million.

Total LTO cartridge shipments were 6.8 million units. LTO–4, the latest generation of the LTO format, accounted for 12% of unit shipments, while LTO–3 accounted for 43% of LTO cartridge shipments and 41% of revenues. Sales of LTO–2 cartridges held steady, accounting for 36% of LTO cartridge shipments and 25% of revenues.

Shipments of DDS cartridges were down significantly in the fourth quarter, at 2.47 million units, with the DAT–72 format accounting for 33% of unit shipments and 51% of revenues. The newer DAT–160 cartridges accounted for 7% of DDS shipments. Hewlett–Packard led the DDS cartridge market with a 49% market share. Overall DDS cartridge revenues topped $17 million.

Shipments of DLT–S tape cartridges were about 780,000 units in Q4, with HP leading this market segment followed by Quantum and Maxell.

Shipments of DLT–V tape cartridges held steady in Q4, at about 480,000 units and $14.72 million in revenues. Hewlett–Packard led this segment with a 23% market share, followed by Quantum with a 16% slice.

AIT cartridge sales were about 380,000 in Q4, with AIT developer Sony holding on to a 96% market share.

Shipments of QIC tape cartridges were only about 190,000 units in Q4, representing about $6.4 million in revenues. Imation dominated the QIC segment with an 86% market share. —DS


Recent tape–related product announcements

By the InfoStor staff

Sun Microsystems recently began shipping a slew of new products designed to store, manage, and secure data for long–term archiving. The latest additions to its archiving portfolio include a midrange tape library, a family of fast–access tape drives, an archiving appliance with tiered storage capabilities, and an open–source key management system to aid in the encryption of archive data. Sun’s new archiving products include the following:

  • The Sun StorageTek SL3000, a midrange tape library based on the same architecture as the SL8500. The SL3000 allows for upgrades up to 3,000 slots without downtime and offers “any cartridge, any slot” technology to enable consolidation and leverage legacy tape media. In addition, the SL3000 allows for multiple partitioning to consolidate existing library assets.
  • A new family of fast–access tape drives designed for nearline archive applications. The T9840D drives have an average data access time up to 4x faster than conventional capacity–centric tape drives, as well as built–in encryption.
  • The Crypto Key Management System (KMS) 2.0, which is Sun’s first key management product to deliver a single, centralized key encryption architecture for multi–vendor tape drives, including HP LTO and Sun StorageTek T9840D and T10000 products. With KMS 2.0,