Tape, as a data storage medium in computers, is a technology that is over 60 years old and was first used to backup data from a Univac I system back in 1951. It continued to be used to back up various large computer mainframe systems that replaced the Univac systems. From there tape based backup migrated to the distributed computing platform as proliferating PCs (Personal Computer) began to be networked together in order to share expensive disk space for storing the data they produced.
A Basic Definition
In IT, tape, also known as magnetic tape or electromagnetic tape, is a readable and writable external storage medium that consists of a loop of flexible celluloid-like material, which is coated on one side with a ferromagnetic type material. It is commonly used for backup, archiving and data collection operations.
The tape is wound on reels, which can be open-reels, such as were used with mainframe systems, or they may be contained in some type of cassette or cartridge as is common today. Data is recorded on the tape by a tape drive, which magnetically encodes tracks on the magnetic coating according to a particular tape format.
A Word about Formats
Over the years, tape has come in many forms starting with the Univac 1200 ft. reels that used a thin ½ in. wide, nickel-plated bronze metal strip. Then IBM came out with 10.5 in. reels using a less expensive ferrous oxide coated ½ in. celluloid type tape, similar to those used for audio recordings, in 1200 and 2400 ft. lengths.
The first series of these IBM open-reel tapes contained seven parallel tracks of data recorded along the length of the tape. A later version upped this to nine parallel tracks of data (8 bits plus parity). In comparison, modern cartridges use 128 or more tracks. The IBM nine-track open-reel tapes became the de facto industry standard for mainframe systems for years until IBM developed cartridge based tape.
Soon other companies also started making cartridge-based tapes in a wide variety of sizes and formats. Some of the more commonly used formats in the late 1990s through the 2000s were IBM 3590/2, DDS (Digital Data Storage – 4mm), AIT, AIT-2 (Advanced Intelligent Tape – 8mm), Mammoth (also 8mm), DLT (Digital Linear Tape) series (I – IV), SDLT (Super Digital Linear Tape) and LTO-1 to 7 (Linear Tape Open 1-7). Today, the LTO format is the most widely used format in distributed computing environments.
How Data is Encoded on Tape
There are several basic methods used to encode or write data to a tape, depending on its format and manufacturer specifications.
- Linear – This method writes data in long parallel tracks that span the length of the tape. Tape drives use multiple heads to write simultaneously these parallel tracks down the length of the tape. This method, which is the simplest, was used in early tape drives. It also has the lowest data density.
- Linear Serpentine – This variation on the linear method uses more tracks than tape heads. Each tape head still writes one track at a time. Once a pass has been completed over the entire length of the tape, the heads all shift slightly and start writing another set of tracks in the opposite direction. This process repeats until all tracks have been written or read. As this method provides many more data tracks on the tape, data storage capacity is significantly higher.
- Scanning – This method writes short dense tracks across the width of the tape rather than along its length. Tape heads are located on a drum or disk, which is perpendicular to the tape path and rotates rapidly while the slower moving tape passes it.
- Helical Scan – This method is a variation of scanning and writes short dense tracks diagonally across the tape.
Tape Capacity and Longevity
There are several important factors that affect tape capacity and longevity, two of which are recording density and coercivity. Over the years, tape manufacturers have worked hard to improve the quality of the magnetic coating on their tapes to increase both its density and its coercivity.
Ferromagnetic materials with higher recording density levels allow more data to be written into the same space. This was usually specified as characters per inch (cpi) or bits per inch (bpi) in the past but is now measured in Gb/in2.
Coercivity is the measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. Obviously if a tape becomes demagnetized, it would lose all data written on it. So the higher the coercivity of a tape, the more resistant it is to becoming demagnetized and the longer it can hold data.
Modern tape drives also now include some type of lossless data compression embedded in their hardware, which further increases the amount of data a tape can hold.
Recent advancements in tape technology, like FujiFilm’s development of Barium Ferrite for the magnetic layer, address the issue of oxidization and significantly increase tape durability as well as capacity. Modern LTO tapes have an archival shelf life of over 30 years and LTO-7 has a native capacity of 6TB or 15TB with compression.
Another significant development in tape is the open source LTFS (Linear Tape File System) for LTO tapes. As discussed in our article, “What is LTFS”, this self-describing tape file system lets LTO-5 and later tapes be mounted and read natively by the operating system. This can provide true data portability without the need for proprietary software.
Today’s LTO-6/7 products are ideal for archive use where large amounts of data must be retained indefinitely at the lowest cost possible. Modern archive solutions greatly simplify tape interaction; moving data to tape is as simple as copying to a network share or an object store bucket. Additionally, where backups are concerned, tape provides a secure, off-line copy of data that is not susceptible to malware or hacking attacks that can affect data stored on disks in the enterprise. It can also help meet compliance requirements.
The Future of Tape
New and ongoing developments in LTO tape technology and reliability insure that it will be a viable storage media for the foreseeable future. The current road map for LTO shows continuing gains in capacity and throughput speeds that are necessary for dealing with the ever-growing amounts of unstructured data. If you don’t have tape as part of your infrastructure today you should explore it, if you do then feel confident that your investment will be useable for decades to come.
Sponsored by Fujifilm Dternity, Powered by StrongBox
This article on “What is Tape?” is one of an ongoing series of articles in the Storage Switzerland “What Is” series. These articles provide a refresher on key fundamentals of various storage technologies, for those who are new to, or considering entering the IT field, and those who simply wish to “brush up” on the basics.