Magnetic tape backups are a form of data backup that stores information on magnetic tape, which is a long strip of plastic film coated with a magnetic recording material (TechTarget, 2023). Tape backups have been around since the early days of computing in the 1950s and became widely used for data storage and backups in the 1960s and 1970s. They allow you to store large amounts of data offline and provide a reliable way to retrieve data in the event of a system failure or data loss.
Magnetic tapes work by writing data to them in the form of magnetized spots on the tape media. The backup software handles compressing and formatting the data so it can be properly written to and read from tape. Tape drives use read/write heads to access the data on the tapes. Robotic tape libraries automate the process of retrieving, writing, and storing tape cartridges.
Overall, magnetic tape backups offer businesses and organizations a way to store large amounts of data offline and recover it when needed. They provide an air gap that protects against cyber attacks since they are offline. Tapes are portable, removable, and can be stored offsite for data protection and archiving purposes.
Advantages of Tape Backups
Tape storage offers several key advantages that make it an attractive option for backup and archival data storage (https://www.salvagedata.com/magnetic-tape-storage-advantages-and-disadvantages/):
Large capacities: Modern tape cartridges are able to store tremendous amounts of data, with capacities ranging from a few hundred gigabytes to 60 TB per cartridge. This allows large volumes of data to be stored efficiently (https://www.nakivo.com/blog/top-tape-backup-advantages/).
Long retention periods: Tape has a longer shelf life than other media, with manufacturer warranties of 30 years or more. This makes tape well-suited for long-term data archiving.
Portability: Tape cartridges are small and rugged, making them easy to transport and store offsite for disaster recovery.
Low cost per GB: On a per-gigabyte basis, tape is significantly less expensive than disk or cloud storage. The cost efficiency makes it feasible to retain large amounts of infrequently accessed data.
Disadvantages of Tape Backups
One of the biggest disadvantages of magnetic tape backups is their slow data transfer rates. Unlike hard disks which provide random access to data, tape drives can only read/write data sequentially from start to finish. This sequential access means locating and retrieving specific data from a tape backup can be very time consuming ([1], [2]).
Another disadvantage is the fragile nature of tape media. Magnetic tape can be easily damaged by physical stress, high temperatures, magnetic fields, and humidity. Damaged tapes can result in irrecoverable data loss unless there are backup copies. Proper handling and storage is crucial for preserving data integrity on magnetic tapes ([3]).
Use Cases
Magnetic tape backups are ideal for long-term data archiving and offline data storage. Tape offers several advantages for archival purposes, including low cost per gigabyte stored, high data density, and long media lifespan and shelf life. Common use cases of tape backups include:
Disaster recovery – Tape backups can be easily transported offsite and stored offline in a secure location. In case of a disaster that destroys the primary data center, the data can be quickly restored from the offline tapes.[1]
Regulatory compliance – Some industries require retention of data for several years. Tape is a cost-effective solution for achieving compliance while storing decades of backup data offline.[2]
Cloud archiving – Tape is complementary to cloud storage for cost-effective long term archiving. Less frequently accessed “cold” data can be stored offline on tape while more active data resides in the cloud.[3]
Overall, tape offers air-gap protection and economical long-term retention for large amounts of infrequently accessed reference data.
[1] https://www.nakivo.com/blog/tape-backup-overview/
[2] https://www.techtarget.com/searchdatabackup/definition/tape-backup
[3] https://corodata.com/tape-backups-still-used-today
Tape Media
There are several common tape media formats used for backups:
- LTO (Linear Tape Open): Perhaps the most widely used format today, LTO tape cartridges come in various generations offering compressed capacities up to 30 TB and data transfer speeds up to 360 MB/s 1. The open LTO format is licensed and developed by technology companies like IBM, Hewlett Packard, and Quantum.
- DAT (Digital Audio Tape): An older tape standard once popular for backups, DAT tapes provided up to 72 GB compressed capacity and transfer speeds around 10 MB/s. DAT has largely been replaced by LTO today 2.
- SDLT (Super DLT): An extension of earlier DLT technology, SDLT tapes provided up to 1.2 TB capacity and speeds up to 43 MB/s. The SDLT format had a relatively short lifespan before being replaced by LTO 1.
- DLT (Digital Linear Tape): An older mid-range tape system used from the late 1990s through mid 2000s, DLT offered compressed capacities up to 800 GB and transfer rates around 10 MB/s before being superseded by SDLT and LTO 3.
Tape Drives and Libraries
Tape drives come in different form factors depending on storage capacity and number of tapes needed. The main options are:
Single Tape Drives
Standalone tape drives like LTO, DAT and SDLT are designed to connect to a server and provide a backup destination. They typically hold a single tape at a time with capacities ranging from 200 GB to 30 TB uncompressed depending on the tape technology. Single drives are a cost-effective option when backup capacity needs are low.
[1]
Autoloaders
Autoloaders are robotic arms that hold multiple tape cartridges and can load them sequentially into a built-in tape drive for unattended backups. They provide more capacity than single drives and are useful for small-scale backups. Autoloaders typically hold between 6 to 24 tapes with capacities from 1.2 TB to 720 TB uncompressed.
[2]
Tape Libraries
Tape libraries are the largest and most advanced form factor, containing multiple tape drives as well as slots to hold dozens or hundreds of cartridges. Their robotic arms can access tapes independently and load them to any drive. Large tape libraries can hold petabytes of data and allow scaling by adding more tape slots and drives. They are used for enterprise-class backup and archiving.
[1] https://en.wikipedia.org/wiki/Tape_library
[2] https://www.techtarget.com/searchdatabackup/definition/tape-library
Writing and Reading Data
Magnetic tape drives write and read data sequentially along the length of the tape. This is known as sequential operation, as opposed to random access storage like hard disk drives or solid state drives. Data is recorded in tracks running the length of the tape. Within each track, data blocks are written in a serpentine pattern – the drive writes from beginning to end of the tape, then reverses direction for the next track. This back and forth movement is similar to a serpentine road or path.
The sequential nature of tape drives means that to access a particular piece of data, the drive may need to scan through large portions of the tape to reach the desired location. However, sequential operation enables streaming data transfers at very high speeds. Tape drives are designed to stream data as fast as possible during backups, recovery, and archiving operations. The downside is that random access is very slow compared to disk drives. Locating and retrieving a small amount of data from a large tape archive can take substantial time.
Modern tape drives continue to leverage sequential recording to provide economical high-capacity storage for backup and archiving use cases where access speed is less critical. Serpentine writing patterns maximize capacity and performance. Careful data management is required to make the most effective use of tape in a tiered storage infrastructure.
Managing and Maintaining Tape Storage
Proper management and maintenance is critical for getting the most value out of tape backups. This involves following best practices around media rotation, refresh cycles, and environmental controls.
Media rotation involves moving tapes through a cycle where they are written to, stored offsite, and retired. Tapes that are actively being written to should be rotated on a frequent basis, such as weekly or daily. This ensures you have recent backups stored offsite in case of disaster. Tapes should also be retired from the rotation based on age and number of passes. Retired tapes can be kept in long term archival storage.
Refreshing tapes on a regular cycle is important to maintain data integrity. Tape media can degrade over time, so tapes in active rotation should be replaced every 2-5 years. Tapes in archival storage can last 10-30 years before needing refreshment. Planning a proactive tape replacement cycle avoids situations where tapes fail due to age.
Proper environmental conditions are critical for long term tape storage. Tapes should be stored in a temperature and humidity controlled environment. Dust, debris, and magnetic fields can also degrade tapes over time. Storing tapes in protective cases and controlled environments reduces these risks.
Following best practices for media rotation, refresh cycles, and environmental controls enables organizations to maximize the lifespan of their tape backups. Proper management is key to ensuring tape backup data remains intact and accessible when needed for restores [1].
Data Integrity
Data integrity is crucial for magnetic tape backups to ensure that data is not corrupted over time and remains intact for recovery when needed. Three key factors impact data integrity with magnetic tapes:
Bit Error Rate (BER) – This refers to the number of corrupted bits when data is read from the magnetic tape. Higher density tapes generally have higher BERs. However, modern tape drives use error correction techniques like Reed-Solomon coding and parity checking to detect and recover from errors and provide astonishingly low BERs. For example, LTO-8 drives have native BERs better than 1 error in 1019 bits read.
Media Durability – Magnetic tape media can retain data for decades if stored properly under recommended temperature and humidity conditions. Enterprise-grade tapes are built robustly and undergo extensive lifecycle testing. LTO tapes for example are verified to sustain over 30 years of shelf life and 5,000 load/unload cycles. Tape vendors provide warranties covering both shelf life and usage durability.
Data Verification – Modern tape drives automatically verify data after writing. LTO drives for example perform a second read pass to check newly written data. In addition, tapes can be read back years later to verify that data remains intact. Cryptographic hash functions like SHA-256 can also be used to produce a checksum to periodically validate data integrity.
Future Outlook
Magnetic tape storage continues to have a strong future outlook, especially for long-term data archiving. Tape capacity and speeds continue to improve dramatically. For example, in 2022 IBM and Fujifilm demonstrated magnetic tape technology capable of storing 580 TB per cartridge, over 10x greater than current LTO-9 cartridges (1). Tape drive transfer speeds are also increasing, with current drives reaching up to 400 MB/s.
Adoption of tape remains high for backup, archiving, and cold storage applications. According to an IEEE article, over 90% of all data is “captured and saved” using magnetic tape (1). Tape’s portability, longevity, and low cost make it well-suited for long-term data preservation. While disk and cloud storage are preferred for hot data, tape provides an ideal cold storage tier. Advances in LTO technology and tape libraries will likely ensure tape remains a critical storage medium long into the future.