How does backup tape work?

Backup tape refers to magnetic tape used for storing copies of computer data as a form of backup. It allows important data to be periodically copied and stored separately as a precaution against loss of the primary data storage. Backup tapes are portable, removable, and provide a way to archive large amounts of data offline. When used as part of a rotational backup strategy, they provide an additional layer of data protection and recovery.

Backup tapes work by writing data from the primary storage device onto a long strip of magnetic tape that is wound inside a cartridge or cassette. Tape drives use a read/write head to store and retrieve the data. Tapes are relatively inexpensive, easy to transport and store offsite. They also have a long shelf life if properly stored. Backup tapes have traditionally been used for large enterprise systems but declined in favorable compared to disk/cloud backups. However, they are still used today in certain situations where removable offline storage and portability are beneficial.

History of Backup Tape

Magnetic tape was first developed as a data recording technology in 1928, when Fritz Pfleumer invented a recording method for magnetizing thin strips of tape coated with iron oxide powder (source: However, magnetic tape did not become commonly used for computer data storage until the 1950s.

One of the first commercial magnetic tape data storage devices was the UNISERVO tape drive, introduced by Remington Rand in 1951. The UNISERVO used large open reels of tape that were about one inch wide, storing a few megabytes per reel (source:

In the 1960s and 1970s, tape technology continued to advance with the introduction of smaller tape reels and cassettes, as well as new tape compositions that allowed for higher recording densities. Key innovations during this period included IBM’s 9-track tape format in 1964, the Laurel LSA tape cassette in 1969, and the IBM 3480 cartridge in 1984, which could store up to 200 megabytes on a single cartridge (source:

The late 1980s and 1990s brought the introduction of helical scan tape drives that increased capacity and performance, as well as new tape formats like DLT, LTO, and Super DLT. Today, LTO remains a widely used backup tape standard, with capacities of up to 30 TB per cartridge as of 2020.

Backup Tape Media

There are various types of magnetic tapes used for backup storage. Some common formats include:

Linear Tape-Open (LTO): LTO is one of the most widely used tape formats today. LTO tape cartridges use a single reel design and come in different generations offering increased capacity. The latest LTO-9 tapes can store up to 45 TB uncompressed data per cartridge.

Digital Linear Tape (DLT): DLT tapes were historically used for enterprise backup and archiving but have been largely superseded by LTO. DLT provided higher capacities than earlier tape formats. The latest DLT-S4 tapes could store up to 800 GB per cartridge.

Quarter-Inch Cartridges (QIC): QIC tapes use two reels and were commonly used for data backup on personal computers. Different QIC standards provide capacities from a few MB per cartridge to multiple GB. They have declined in favor of LTO and other formats.

Tape materials have evolved from older metal particle and metal evaporative tapes to modern advanced metal particle tapes with higher density capabilities. Tape cartridge capacities range from hundreds of GB to tens of TB depending on the format and generation. Higher capacity tapes allow storing more backup data per cartridge.

How Data is Stored

Data is stored on backup tape using a linear method, meaning it is written sequentially along the length of the tape from beginning to end (1). This is different from hard disks and solid state drives, which allow random access to data. Tape drives use servo tracks running the length of the tape to guide the read/write heads and keep them aligned (2). As data is written, the servo tracks provide reference points so the drive knows where data blocks are located on the tape.

The linear method of writing data has implications for how backup tapes are used. For example, to access a file near the end of the tape, the drive may need to scan the entire length of tape from the beginning to reach that file’s location. Tapes are designed for sequential access rather than random access. During a restore operation, tapes are generally read from start to finish.

The linear format maximizes storage density on tape. By tightly packing data blocks end-to-end without wasted space, each tape cartridge can store terabytes of data (1). The servo tracks take up very little area, allowing nearly all of the tape’s surface to be used for storing data.


Tape Drives

Tape drives are devices that read and write data onto backup tape cartridges such as LTO (Linear Tape-Open). They use servo tracking to guide the tape heads and accurately locate data tracks on the tape. The two main components of a tape drive are the tape head, which reads/writes data, and the tape transport mechanism which controls tape movement. Tape drives use a helical scan recording method to write data diagonally across tape tracks. This allows for efficient and high capacity storage. Newegg Business

Modern tape drives like LTO-8 can store up to 30TB of uncompressed data on a single LTO cartridge. They are available as standalone internal/external drives or integrated into automated tape libraries which manage multiple tapes. Tape libraries with multiple drives provide increased throughput for backing up large amounts of data. High end tape drives offer data transfer speeds over 300MB/s compressed. Key tape drive manufacturers include IBM, HP, Quantum, Oracle, Spectra Logic and Qualstar.

In summary, tape drives provide reliable and scalable data storage using removable tapes, making them well-suited for long term data archiving, backup and disaster recovery. Their speed, capacity and affordability continues to improve with new standards like LTO-8.

## Reading/Writing Data

Tape drives read and write data sequentially along the length of the tape. This means the drive must physically wind the tape from one reel to the other in order to access different sections of data. The drive contains read/write heads that make contact with the tape as it moves across them. These heads can magnetically read or write binary data to the tape.

To write data, the tape drive receives the data from the backup software and converts it into binary code. The drive then magnetically encodes this binary data sequentially across the length of the tape as it moves over the write head. The drive winds the tape along until the entire backup is written.

To read data, the tape is rewound to the correct position. As it moves over the read head, the changes in the magnetic field are detected and converted back into binary data. The drive then sends this binary data to the backup software, which assembles the bytes in the proper order to recreate the original backed up files and folders. This process continues sequentially until all requested data has been read.

Compared to random access storage like hard disks, tape drives are slower to access specific data because they must physically wind and unwind past irrelevant sections first. However, their sequential operation means large volumes of data can be read or written very quickly in a single pass.

Advantages of Backup Tape

Backup tape has several key advantages that make it an attractive option for data storage and archiving.

One of the biggest advantages is the low cost. According to Nakivo, tape backups are highly affordable when looking at cost per gigabyte compared to disk or cloud backups. The media itself is inexpensive and storing data on tapes for long periods of time is very cost effective.

Long shelf life is another advantage of tape. Tapes can store data safely for 10-30 years if stored properly. This makes tapes ideal for archival purposes where data needs to be retained and accessible for many years. Tape durability and longevity exceeds other backup media.

Backup tapes also provide excellent portability. The small size and light weight of tapes allows them to be easily transported and stored offsite for protection against disasters or malfunctions. This portability also enables easy physical transfer of large datasets across locations.

In addition, tapes offer impressive security for data at rest. They are not continuously connected to a network, minimizing exposure to cyberattacks. Encryption provides an extra layer of protection. The linear format of tapes also makes searching and accessing specific data very difficult for unauthorized users.

Disadvantages of Backup Tape

Backup tape has some notable disadvantages compared to other backup media like disk drives or cloud storage. Three major drawbacks are:

Slow speed – Tape drives are relatively slow, with typical data transfer rates of around 160 MB/s when reading or writing. This is much slower than hard disk drives or SSDs which can transfer data at over 500 MB/s. The sequential access nature of tape, where data is accessed linearly from start to finish, makes locating and retrieving specific files slow compared to random access storage.

Limited capacity – The maximum native capacity of tapes today is around 15 TB for the high-end formats like LTO-8. While tapes can hold a decent amount of data, disk drives provide much more end-to-end capacity for ongoing backups, with disks up to 18 TB – but of course cost is higher. Cloud storage offers essentially unlimited capacity.

Vulnerability to damage – Tape media is physically vulnerable, where improper handling, exposure to magnets, or environmental issues can damage tapes and make recovery difficult. Tapes also have a finite shelf life of around 30 years. Disk drives and cloud storage offer more resilience and redundancy options.

So in summary, while tapes are inexpensive, they suffer in transfer speed, total capacity limits, and durability compared to other backup options.

Use Cases

Backup tape is commonly used for long-term data storage and archiving in data centers and cloud environments due to its high capacity and low cost per gigabyte. Tape cartridges can store terabytes of data and have a shelf life of 30 years or more if stored properly.

According to Backup to Tape in 2023: What, How, and Why, over 80% of all backup data is stored on tape because of its affordability. Tape allows companies to retain years of backup data offline while only paying to periodically retrieve and re-archive it.

Tape is also used for migrating data to and from the cloud. The portability of tape cartridges makes transporting large datasets efficient compared to transferring over networks. Tape offers a reliable option for transporting sensitive data to off-site locations for disaster recovery purposes.

Media companies and studios utilize tape for archiving large video and audio assets. The high capacities allow fitting entire libraries on a small number of tapes. While retrieving the data may be slower than disk, tapes provide cost-effective long-term storage.

Future Outlook

The future of tape backup appears to be positive, with consistent advancements in capacity and performance. Tape has continued to evolve and remains a viable long-term storage option even in today’s digital world [1]. Cloud providers are increasingly adopting tape for cost-effective cold data storage. Amazon Web Services offers Amazon S3 Glacier which utilizes tape [2]. Tape’s roadmap is defined by the LTO (Linear Tape Open) standard, currently on its 9th generation. LTO-9 offers a native capacity of 18TB per cartridge with up to 900MB/s transfer speeds [3]. As capacity and density continue improving, tape will have an ongoing role for affordable long-term archival storage. Its portability also makes tape ideal for off-site data protection and disaster recovery needs.