Introduction
Tape drives are a type of data storage device that uses magnetic tape to store and retrieve digital information. They were first introduced in the 1950s and have been used for over 60 years as an efficient way to back up and archive data offline. Some key benefits of using tape drives for data storage include their high capacity, low cost, longevity, portability, and security. However, accessing data stored on tape can be slow and requires dedicated hardware.
Tape drives work by writing data to long reels of magnetic tape in linear tracks. The data is stored by magnetizing spots on the tape surface to represent binary 1s and 0s. Modern tape cartridges can hold anywhere from a few hundred gigabytes up to 240 terabytes uncompressed. This makes tape ideal for securely storing large amounts of infrequently accessed data over long time periods.
While tape drives offer massive amounts of inexpensive storage, they are sequential-access devices. This means data has to be read from the beginning to end of the tape to locate a specific file, which is a slow process. Tape drives also require compatible hardware like a tape library or autoloader to function. So accessing data on tape has some challenges compared to faster random-access storage like disks or flash memory. Overall tape remains an important medium for cost-effective long-term data archival and backup.
Brief History of Tape Drives
Magnetic tape was first used for data storage on mainframe computers in the 1950s. Tape drives used open reels of tape that stored a few megabytes of data. The first tape drive, introduced by IBM in 1952, was called the IBM 726 and could store about 2.3MB of data on a single reel of tape (https://www.ironmountain.com/resources/blogs-and-articles/t/the-history-of-magnetic-tape-and-computing-a-65-year-old-marriage-continues-to-evolve).
In the 1960s and 1970s, capacities increased and cassettes replaced open reels. IBM introduced the IBM 2400 series tape drives which could store up to 100MB per tape. The 3480 cartridge tape system launched in 1984 could store up to 200MB per cartridge (https://www.computerhistory.org/storageengine/tape-unit-developed-for-data-storage/).
Tape drive capacities continued to grow over the decades, into the gigabytes and then terabytes. Modern tape drives like LTO-8 can store up to 12TB uncompressed on a single cartridge (https://en.wikipedia.org/wiki/Tape_drive). Tape remains heavily used for backup and archiving, especially for large data sets.
How Tape Drives Store Data
Tape drives record data onto magnetic tape using different methods depending on the type of tape drive. Traditional tape drives use a serpentine recording method where the tape passes back and forth over the read/write heads in a zigzag pattern. The heads physically touch the tape to read and write data in diagonal strips across the width of the tape.
Newer linear tape drives use a linear method rather than a serpentine pattern. The tape moves in a straight line past the read/write heads, which hover above the surface of the tape without touching it. This linear method allows for higher recording densities.
There are two main tape formatting standards that differ in how data is written to the diagonal strips on the tape:
– Helicoidal scan tapes use a helical scan method where the heads spin at an angle across the width of the tape. The diagonal strips overlap slightly to prevent gaps in the data. Video cassettes commonly use helicoidal scanning.
– Linear serpentine tapes maintain the straight linear motion of the tape. The heads write data in straight diagonal strips across the tape. There is unused space between the strips. Linear serpentine is used in data backup tapes like LTO and DAT.
Linear serpentine tapes allow for faster data access while helicoidal tapes provide higher data density but slower access. Most modern tape drives use linear formatting.
Tape Drive Interfaces
Tape drives connect to computers and servers through various interfaces that determine the speed and compatibility of data transfer. Some common tape drive interfaces include:
- SAS (Serial Attached SCSI) – SAS is a common serial interface for connecting drives in servers and data centers. SAS tape drives can achieve speeds of up to 12 Gbit/s for fast data access.
- Fibre Channel – Fibre Channel is a high-speed network interface commonly used with SANs (Storage Area Networks). Fibre Channel tape drives can reach speeds of 16 Gbit/s and higher.
- SATA – SATA (Serial ATA) is a common interface for connecting devices inside computers. SATA tape drives are slower than SAS or Fibre Channel, with maximum speeds of 6 Gbit/s.
- USB – USB (Universal Serial Bus) is a common plug-and-play interface for connecting peripherals. USB tape drives are portable but slower, with maximum speeds of 480 Mbit/s.
When selecting a tape drive, it’s important to consider the interface type and speed to ensure proper compatibility and performance for your storage needs. SAS and Fibre Channel interfaces are best suited for data centers and servers, while SATA and USB work for personal backups and archives. Refer to vendor specifications to match interface speeds and connector types.
Most modern tape drives support bridging between SAS and Fibre Channel ports. This allows connecting tape drives to either interface type, adding flexibility for different storage environments.
Accessing Data on Tape
Tape libraries and autoloaders are commonly used to access data stored on tapes. Tape libraries contain multiple tape drives and use robotic mechanisms to mount and unmount tapes into the drives automatically. This allows large volumes of data to be accessed efficiently. Autoloaders are simpler, smaller capacity versions of tape libraries that contain just one or two tape drives.
To read data from a tape, the drive must physically position the tape and align the read/write heads with the correct data tracks. Tape drives use servo positioning systems to achieve precise alignment of heads and data tracks. The servo tracks provide feedback to control motors that manipulate the tape position. Once aligned, the read heads can detect the magnetically encoded data and convert it into digital information.
Newer tape drives often have multiple read/write heads to increase performance. Grouping data into efficient block sizes also helps maximize throughput when reading from or writing to tape.
Reading Data from Tape
Data is stored sequentially on magnetic tape media. To access a particular file, the tape drive must locate the correct position on the tape where that file begins. This requires winding or rewinding the tape until the read/write heads are aligned with the start of the requested data.
When reading a file, the tape drive starts reading at the beginning of the file and continues sequentially until reaching the end. Tape drives cannot randomly access data like hard disk drives. This sequential access means reading times are directly proportional to the location of the data on tape. Starting and stopping the tape to locate filemarks adds considerable time to read operations.
Data on tapes is organized into blocks with filemarks denoting the start and end of each file. When reading, the drive positions to the start of a block and reads all data sequentially until hitting the next filemark. The driver software then assembles the blocks into the original file. Choosing appropriate block sizes improves performance by minimizing unnecessary tape stops and starts.
According to the IBM System Storage Tape Drive and Media Knowledge Center, efficient blocked reads are achieved when “the block size is larger than the internal record size, up to a point. Larger block sizes result in fewer interrupts to the host system.” They recommend blocks of at least 32KB if possible.[1]
Advanced Tape Features
Modern tape drives offer advanced features to increase capacity and usefulness.
Compression
Tape drives use compression to fit more data onto each tape. Data compression reduces the physical size of data by identifying and encoding redundant patterns. The most common tape compression methods are LZO and LZ4, which provide fast compression speed with reasonable compression ratios (TechTarget). Higher compression allows more data to be stored on tapes.
WORM Tapes
Write-once read-many (WORM) tapes cannot be erased or overwritten once data is written. This makes them useful for archiving and data retention applications where tampering and deletion need to be prevented. WORM tapes are often used for compliance and regulatory data retention (Wikipedia).
Partitions
Some tape formats allow partitioning a single tape into multiple separate volumes. For example, LTO tape drives support partitioning into two distinct volumes on one tape cartridge. Partitions enable logical separation of data sets and efficient use of capacity (PC Tech Guide).
Managing and Maintaining Tapes
Proper management and maintenance is crucial for getting the maximum lifespan and performance out of tape drives. Here are some best practices:
Tape cleaning: Tape heads need to be cleaned regularly to remove any accumulated debris. Cleaning frequency depends on usage levels. For example, IBM recommends cleaning DAT drives after every 8 hours of tape movement when using IBM cartridges [1]. Using lower quality tapes may require more frequent cleaning.
Environmental conditions: Tapes should be stored in a temperature and humidity controlled environment per manufacturer recommendations, generally around 70°F and 40-60% relative humidity. Magnetic fields should also be minimized. Tapes exposed to extreme conditions or field fluctuations may have degraded performance or permanent damage.
Tape rotation and retention: Regularly rotating tapes helps distribute wear evenly across your tapes. Retiring and replacing tapes after 3-5 years can help avoid issues with older tapes. Maintaining a tape retention schedule also ensures you have recovery points available as needed while recycling tapes in a timely manner.
Alternatives to Tape Drives
While tape drives have been a staple for data backup for decades, newer technologies like disk and cloud storage are emerging as alternatives. Each has its own advantages and disadvantages compared to tape.
Disk-based backups, using external hard drives or NAS devices, provide faster backup and restore times than tapes. However, the upfront cost of purchasing disks can be higher, and there are risks of data loss if multiple disks fail. Disks may require more oversight for media refreshing as well. According to Evolve IP, disk has faster restore speeds of up to 100x that of tape.
Cloud-based object storage like Amazon S3 offers highly durable and scalable offsite data storage. But cloud services come with monthly fees, slower recovery times, and reliance on internet connectivity. BlueXP notes cloud storage can provide faster data access than physical media like tape.
For very large data sets or cold data that is rarely accessed, tape is still preferred by many organizations. Tape’s portability, long shelf life, and offline nature make it advantageous for archival needs. Regulation and compliance also favor tape’s physical controls. According to BackupAssist, REV drives can match or exceed tape on cost for some use cases.
Conclusion
In summary, magnetic tape storage has come a long way since its inception in the 1950s. Key advancements in capacity, speed, reliability and durability have enabled tape to remain highly relevant for backup, archival and cold storage use cases. While discs and flash outperform tape for primary storage, tape offers unmatched longevity, energy efficiency and cost savings for rarely accessed data.
Today, LTO-9 provides native capacity up to 18TB per cartridge and transfer speeds reaching 400MB/s. Enterprise tape libraries scale to exabytes of compressed capacity. Tape is suited for 30+ year retention requirements common in regulated industries. Cloud, HPC and cold data storage provide ample demand for tape. Advanced features like LTFS, WORM and encryption reinforce security and accessibility.
Looking ahead, upcoming LTO-10 to -12 roadmaps and innovations like BaFe and barium zirconate will push native capacities above 100TB. Increased bit densities, multi-actuator arms in drives and expanded automation in libraries promise further speed and reliability gains. While facing competition from high-capacity HDDs and QLC flash, tape will continue playing a key role in the storage hierarchy thanks to its unmatched price per TB and energy efficiency.
