Magnetic tape is one of the oldest technologies for electronic data storage.
Tape has largely been displaced as a primary and backup storage medium, but it remains well-suited for archiving because of its high capacity, low cost and long durability. It is a linear recording system that is not good for random access. If the tape is part of a library, robotic selection and loading of the right cartridge into a tape drive adds more latency. In an archive, such latencies are not an issue. With tape archiving, there is no online copy for quick retrieval, as everything is vaulted for the long term.
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While tape can't compete with other media in terms of random access, there are still industries where magnetic tape storage is the preferred technology:
- Many motion picture production companies record their shoots to tape after experiencing costly failures with both disk and flash.
- Scientific experiments that produce mass quantities of data in a few microseconds leverage tape's capacity and write speeds.
- The oil and gas industry has used tape for years to capture, transport and store valuable data. Because oil exploration occurs outside the data center, tape is a good medium for transporting data back from the field.
Tape is often paired with object storage to address the need for lower-latency file access. Sometimes, it is entirely replaced by object storage.
How magnetic tape works
Data bits -- magnetic states representing on and off -- are recorded to a particulate medium bonded to a substrate of Mylar plastic. Improvements in track-following technology and giant magnetoresistive read/write heads have increased the number of tracks that can be recorded on a tape.
The industry has largely moved from oxides as a recording material toward barium ferrite, which is capable of delivering high recording densities because of its support for perpendicular magnetic recording. Barium ferrite is used in both enterprise tape from Oracle and IBM, and Ultrium format tape from the LTO Consortium.
Top vendors and types of tape
Linear tape open (LTO) is the most popular tape format on the market, although enterprise tape supports greater capacity per cartridge. LTO-7, released in 2015, has a raw capacity of 6 terabytes (TB).
Hewlett-Packard, IBM and Seagate -- which later sold its tape business to Quantum -- formed the LTO Consortium in the late 1990s as an alternative to Quantum's proprietary digital linear tape format. Launched in 2000, the first generation, LTO-1, held 100 gigabytes (GB) of data per cartridge. The consortium has since released a new generation of LTO tape every two or three years, each essentially doubling storage capacity. Throughput speed has increased as well. Each new generation of tape drives can also read tapes back two generations and write to the previous one. Write once, read many (WORM) technology, storage encryption and partitioning are all supported starting with LTO-5.
IBM and Oracle lead the pack of enterprise tape providers. Like LTO, these tape technologies are also based on barium ferrite media, but provide drive technology innovations, tape lengths and cartridge formats that work for their customers. For example, the IBM 3592 Jaguar series tape system leverages its TS1150 drive and claims an uncompressed storage capacity of up to 10 TB. Oracle, which bought Sun Microsystems and StorageTek tape, has been building on a tape technology line called T10000 since 2010, offering a T10000D drive and cartridge with a native, noncompressed capacity of 8.5 TB.
Magnetic tape vs. disk vs. cloud storage
Disk surpassed tape as a preferred backup media in the late 1990s. Recent innovations in the tape world, including IBM's Linear Tape File System (LTFS), have made it easier to access data on tape. Files and objects can be copied directly to a tape repository running LTFS technology, so they retain their native structure and metadata.
Tape is faster than disk when performing streaming read/write operations, but content on magnetic tape can only be read or written in a sequential format by spooling it to the appropriate position. In contrast to disk, where access times are measured in milliseconds, tape access times can be seconds or minutes long. As a result, serial access can be good -- streaming speed for LTO-7 is approximately 300 megabytes per second (MBps) -- but timely random access is almost impossible to achieve.
Cloud providers have embraced tape for long-term data retention. For example, Amazon Glacier has a strong tape component. And Google has incorporated tape for disaster recovery -- when Gmail went down for three days in 2011, the company rescued the system using tape backup.
Magnetic tape storage best practices
Magnetic tape cartridges are resilient, but still require proper care. Although the lifespan of a tape is expressed in years, careless handling can cut that to weeks or destroy a tape completely.
Dust, dirt and oils are harmful to tape. Users should keep tapes in their plastic cases when they are not in use. In addition, users should not:
- Handle the tape directly;
- Touch the tape surface; and
- Open the drive doors manually.
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Margaret Rouse asks:
How do you use tape in your data storage environment?
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