It is not uncommon to see many different technologies in the data center, including disk, tape and even optical solutions. Each of these solutions provides unique benefits from a performance, reliability and availability perspective. However, one technology that often gets shortchanged is tape, and some people continue to think that tape is an outdated technology unchanged since the 1980s.
The reality is quite different; just as we have seen innovation throughout the data center and ever increasing storage and computing capacities, tape also has advanced at a rapid pace. With that said, there is no technology “silver bullet.” While tape provides important benefits, it must be part of a total data management infrastructure that incorporates other technologies, such as disk and even cloud.
Benefits of tape
Tape technology offers a number of valuable benefits:
1. Write accuracy. The key metric for write accuracy is bit error rate, or BER. BER sounds like a complex concept, but it isn’t. It is simply a measure of the total number of expected erroneous bits as compared with the total number of bits received. In the most simplistic terms, it quantifies the likelihood of a faulty bit as a percent of total number of bits written.
The table below from the LTO (Linear Tape-Open) website, http://bit.ly/QmdDZr, highlights how the BER of tape compares with that of disk storage. As the table illustrates, tape has at least a tenfold improvement in BER versus the most expensive enterprise disks. However, since LTO is normally used for backup and archiving, SATA (serial ATA) has historically been the disk alternative of choice. In this case, tape’s BER is 100 times better. In summary, the likelihood of tape writing an incorrect bit is between 10 times and 100 times better than with an equivalent disk drive.
2. Write verification. Any medium poses a risk that what you want to write does not actually get written. Why would this “silent corruption” occur? Well, it could be caused by a number of things, but it is often related to an unexpected error in the storage hardware.
LTO tape incorporates technology to directly address this risk. As described in the article available at www.lto.org/technology/primer3.html, LTO drives natively reread data as soon as they are written to validate accuracy. This is powerful because this error checking occurs with every write without any need for user intervention. Furthermore, any errors experienced are addressed in real time.
If you compare this with disk arrays, the situation gets murky; each disk vendor has a unique RAID (redundant array of inexpensive [independent] disks) algorithm that may or may not include verification. Some arrays may go back at a later time to “scrub” the disk for errors, but the delayed analysis misses the real-time verification and correction that LTO provides.
Simply put, when you write data to LTO, you can be confident that the tape is accurately storing your information.
3. Cost. Data are growing rapidly, and Framingham, Mass.-based IDC, a global provider of market intelligence, advisory services and events for the information technology, telecommunications and consumer technology markets, based in estimates that data will double nearly every two years (http://bit.ly/Q7LXrE). This is a significant burden on today’s IT environments from both a management and upgrade cost perspective. Traditionally, this information has been stored on disk; but, as data grow, companies need to consider alternatives.
Tape can radically alter the economics of data storage. The Clipper Group, Rye, N.H., published a report titled “Revisiting the Search for Long-Term Storage – A TCO Analysis of Disk and Tape,” available at http://bit.ly/1t1XYOq, that found that tape costs 26 times less than an equivalent disk subsystem with one of the biggest differences being energy cost, where tape is 105 times less than disk. Clearly these are compelling numbers and implementing tape can dramatically affect the economics of data storage, especially with older, less frequently accessed information.
4. Long-term data accessibility. Extended data retention is the norm in today’s IT environments. Yet, as retention extends, users need to be cognizant of the consistent readability of their storage medium.
Bit rot refers to the gradual degradation of magnetic media that can happen over time and can result in data corruption. Noted industry Analyst W. Curtis Preston discusses this concept in a blog post titled “Tape more reliable than disk for long term storage,” available at http://bit.ly/1kqeG64.
The long and short of it is that all magnetic media face the risk of bit rot, but disk faces a higher risk than tape because of its smaller magnetic particles and higher operating temperature. Thus, customers can be more confident of the long-term viability of data stored on tape versus disk. Additionally, this formula helps explain why LTO tapes are stated to last 30 years while the average disk subsystem is replaced every five years.
Taped off
Tape technology provides clear benefits as described, but it is not a panacea. Tape, while quite fast, is optimized for accessing very large pieces of data, which is common in applications such as backup and archiving. However, many traditional applications, such as email and databases write data in smaller pieces that can lead to reduced performance with tape and, thus, it typically does not make sense to store active application data on a tape infrastructure.
Another consideration with tape is that there also can be a delay in accessing stored data as the media must be loaded into a tape drive prior to reading or writing information. This is rarely an issue for inactive data, such as backup and archive, but is less optimal for primary applications.
Tape is an ideal part of an IT infrastructure because of its low cost and high levels of availability. It brings a different access profile than disk and typically is used for less frequently accessed information, such as older files, backups or even data archival. In this way, it is clearly a powerful and complementary solution to disk storage because disk brings the instant random access that today’s high performance applications require.
It is clear that tape provides compelling benefits. Some vendors might suggest that the real question is “Should I use disk or tape?” and often this binary approach is driven by vendors who primarily sell disk technology. In my view, that is the wrong question to ask.
The right way to think about it is to ask, “What is the right technology to address my business requirements?”
Frequently, the answer to this question is a combination of solutions, with disk being used for the active or “hot” data and tape used for the older and less frequently accessed information.
The author is director of product and solutions marketing at Iron Mountain, headquartered in Boston, and has more than 10 years of experience working in the data protection industry.
In reel time: For more information on tape storage, visit http://bit.ly/1t1XFTA.
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