00% Disk for Data Protection? by Jay Livens

Disk plays an important role in data protection due to its ability to provide random access to data and consistent performance. Disk vendors are quick to highlight these benefits and often encourage users to rely exclusively on spinning disk and avoid other technologies like tape. Is this a good strategy? Well, if you are a disk vendor, the answer is clearly yes, but is it the right approach to achieve your long-term IT infrastructure and business goals? Invariably, the answer is no. For most users, the best strategy incorporates disk and tape to take advantage of the strengths of each medium. Let's look at some reasons why tape continues to play a critical role data in protection alongside disk subsystems.

Cost Historically low cost has been a hallmark of tape. This leadership continues even with the latest deduplication technologies. For example, noted industry analyst W. Curtis Preston compared the cost of disk vs tape and estimated that storing 20PB of data on tape was more than 20x less expensive than storing on deduplicated disk. The cost considerations extend beyond acquisition and must incorporate operational elements such as power and cooling. These expenses can add up and if you replicate for DR then they are doubled! Tape, in contrast, is very energy efficient. Tape drives and libraries only require meaningful power and cooling when data is being accessed (e.g. tape drives are operating) and very little when the system is idle.

Backwards compatibility Data growth naturally leads to increases in backup data and retained information. Extended retention periods often transcend the lifespan of individual disk or tape hardware. For example, the typical life of a disk array is five years and so a ten year data retention would require that you replace the system twice thus migrate data on two separate occasions. LTO technology will eventually require migrations as well, but the technology provides backwards compatibility for two generations. (Example: LTO-6 can read/write LTO-6 and LTO-5 and will read (but not write) LTO-4.) In ten years, LTO will go through approximately three revisions and as a result you will be able to maintain your investment in LTO technology throughout the entire period.

Air gap A key element in protecting data is ensuring that it is stored in a safe and secure environment where it is immune from hardware failure, viruses, hacking and other negative activities. In the world of tape, this level of protection is easily achieved by encrypting tapes and removing them from the library. An encrypted tape stored on a shelf (or even better in a secure vault!) is immune to these risks. In contrast, a disk subsystem is always online and typically accessible via its management or storage interfaces. This separation of data and access or Air Gap creates a level of protection and security with tape that is difficult if not impossible to match with traditional disk subsystems. A simple example is the challenge of a firmware upgrade. When you upgrade the firmware, there is risk that a catastrophic failure could occur. In so doing, all your online data could be lost. If you were upgrading your tape drives firmware, a catastrophic failure would result in an unusable drive while your data would remain intact.

Long-term reliability Longer and longer retention periods are becoming the new normal as companies are forced to maintain information for legal, regulatory or business intelligence purposes. This extended outlook has made many pundits look carefully at the longevity and accessibility of data stored on different media. Tape provides long-term reliability and consistency and LTO technology supports a thirty year shelf life. The lifespan of disk drives is often much less with a typical life of five years. Horison Information Strategies wrote a paper summarizing the published bit error rates for disk and tape and found that LTO error rates are roughly 1,000x less than SATA disk.

Vendor neutrality The one constant in the data center is change. We frequently see new storage technologies such as SSDs, SAS or even storage virtualization and often many of the biggest innovations are driven by smaller vendors. A key challenge is that each storage solutions is proprietary and uniquely read/writes data. Hence, a SATA drive written by a Data Domain system cannot be read by an HP StoreOnce system and vice versa. This challenge leads to a reduction in flexibility and vendor lock-in. LTO tape is different. It is a standard format and technology across the industry, so an LTO tape written by a tape library sold by HP would be equally readable by libraries sold from any other vendor. This provides users with the flexibility of choosing the right library and technology to meet their business requirements and to avoid disk-style vendor lock-in.

Scalability As data grows, users will naturally need to either increase system performance to maintain backup windows or add capacity to support retention. Two dimensional scalability is a fact of life when it comes to data protection. The challenge is that most disk options provide only limited capacity and performance growth potential. The result is that companies are often faced with the difficult choice of adding multiple independent disk backup systems or costly forklift upgrades to existing systems. Tape provides significantly greater flexibility with the ability to add capacity by inserting more tapes in the library or performance by adding more tape drives. This two dimensional scaling is inherent in tape and allows for more cost effective expansion to meet changing business requirements.

Clearly tape provides strong benefits to backup and recovery. There is no doubt that disk also plays a critical role for data protection, but the two technologies are complementary and are best used together. An integrated st

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