In December 2020, IBM Research and Fujifilm presented a prototype LTO cartridge for 580 terabytes… A small cassette with a magnetic tape holds information like several tens of ordinary HDDs or 120,000 DVDs.
Magnetic tapes appeared almost a century ago, and computer files have been recorded on them since 1952. Our mothers in Soviet research institutes also changed mainframe coils. And in 2021, tapes remain the cheapest drive, with storage costs about 6 times lower than HDDs. Since film has virtually disappeared from the consumer market, many people don’t even know how rapidly this technology is developing.
Reels with magnetic tapes produced by Orwo (GDR) in the Soviet mainframe computer ES-1020 at the Department of Applied Mathematics of Physics and Mathematics of the Leningrad Polytechnic Institute, mid-1980s. The read / write speed was 2 meters (64 kilobytes) per second, a source
A bit of history
In general, the German chemist Fritz Pfleumer invented magnetic tape in 1928, that is, 93 years ago. He was the first to think of spraying with a magnetic powder of iron oxide on thin paper using glue. The first tape was made by the German concern BASF. At first, it was used to record sound, and in the 50s, experiments began on recording video, as well as digital computer data, and the second use case was considered much more promising, because magnetic videotapes still could not compare with film in terms of image quality.
The world’s first digital data tape was recorded and read by magnetic heads Uniservo I for the UNIVAC I computer in 1951. That tape was half an inch (12.65 mm) wide and recorded data at 100 characters per inch.
Uniservo I magnetic heads
Then IBM got down to business, which released 7-track tapes of the same half-inch width.
Then were developed 9-track tapes for IBM System / 360. Nine tracks made it possible to write exactly one byte in each tape position (8 information bits plus 1 control). These coils became the computer standard for a long 30 years, including for Soviet computers.
IBM 2401 drives for System / 360 computers
The recording density grew steadily: up to 200, 556, 800 cpi, then for 9-track tapes it was 800, 1600 and 6250 bytes per inch. By the 70s the recording had reached such a density that it became possible to reduce the tape width. This is how the first compact cassettes and cartridges appeared.
The QIC (Quarter Inch Tape Cartridge) standard was introduced by 3M in 1972, Journey234
Linear Tape-Open (LTO) is one of the modern cartridge standards for maximum recording density.
Current belts are manufactured with a barium ferrite (BaFe) coating. With each new generation of LTO, the particles became smaller and smaller, assembling into narrower data tracks. In December 2020 Fujifilm and IBM announced the first model with a strontium ferrite (SrFe) coating. Particle size decreased by 60%.
Left: the structure of the tape. Right: Photographs of barium ferrite and strontium ferrite particles in the coating. Image: Fujifilm
The density of recording in tapes can be compared to that of HDDs, because it uses a similar principle of storing magnetized bits in a media layer on a substrate.
The density of recording on HDD in the last decade has increased by 9% per year, and for film by 34%. Slide from IBM presentation
HDD write density has slowed growth in the past decade. Great hopes are pinned only on thermomagnetic recording (HAMR), where the indicator exceeds 2 Tbit / in²… LTO is far from such indicators.
But even with the existing density, the cartridges significantly outpace the HDD in terms of the total amount of information, because the area of the tape on the reel is much larger than the area of the pancakes in the hard drive. The design of the cartridge allows 32 readheads to be used simultaneously, which gives an advantage in read and write speed compared to HDD.
The main thing is that the density of recording on tape continues to grow exponentially, at about 33% per year. That is, the doubling of the storage capacity occurs approximately once every two to three years. In comparison, progress in hard drive manufacturing has slowed dramatically (if HAMR fails).
|Recording density (Gbps per inch²)||6.67||29.5||85.9||123||201||317|
|Cartridge capacity (TB)||8||35||154||220||330||580|
|Track width||1.5 μm||0.45 μm||0.177 μm||0.14 μm||103 nm||56.2 nm|
|Linear density (bits per inch)||400,000||518,000||600,000||680,000||818,000||702,000|
|Magnetic layer material||BaFe||BaFe||BaFe||BaFe||CoPtCr-SiO2||SrFe|
|Film thickness (μm)||6.1||5.9||4,3||4,3||4.7||4,3|
|Film length (m)||890||917||1255||1255||1098||1255|
Increase the recording density and capacity of LTO cartridges. A source: IBM
It turns out that film cartridges are now a more promising technology than hard drives. The film is developing, the market is growing, the developers do not spare money for research and make plans for decades to come.
Features of the tape
Tape drives have a relatively long guaranteed data retention life. Manufacturers of modern LTO cartridges usually guarantee data retention for 15 to 30 years.
The device of the cartridge is, in principle, simpler than that of SSD and HDD, where a mechanism for reading and writing information is built-in inside drive, and this mechanism is extremely complex and prone to breakdown. For example, a common reason for failure of SSD and HDD is electronics failure in the controller, and in the HDD there is also damage to the head. In this case, film cartridges are not in danger. The probability of errors when writing or reading a tape is 4-5 orders of magnitude lower than that of hard drives.
Another advantage of cartridges is safety, because drives physically isolated from the network.
If we compare the cost of storing 1 megabyte on different drives, then after exceeding a certain amount of data, magnetic tape is the most profitable option. For example, for $ 500 you can buy a dozen LTO-8 cassettes, 12 TB each. For comparison, HDDs of the same size will cost about $ 3000.
True, the LTO-8 drive itself costs several thousand dollars, so on small volumes the costs will not pay off. As a low-budget alternative, you can buy a $ 95 used LTO-2 drive with 200GB cassettes for $ 8, but this is an eerily outdated lowtech.
MagStor LTO-8 HH SAS (LTO-8) external drive for desktop costs $ 3300
Unlike households, in corporate vaults, the benefits are clear. Additional savings are achieved by reducing the capital cost of building the storage facility, reducing administrative costs and reducing electricity bills, since the storage of cassettes does not require power as is the case with servers. Cm. Cost of Ownership Calculator (TCO) for a corporate data center.
DVDs are not even considered in such systems. For example, it takes a hundred Blu-ray discs at a ridiculous write speed to store at least 5 TB.
Read and write speed
Rewinding a tape is a mechanical process that cannot be done in milliseconds. Imagine that you need to rewind 200 meters of tape to find a file … In general, in modern LTO cartridges, the tape length exceeds 1 kilometer. Therefore, the average access time to data is tens of seconds, while hard drives have from 5 to 10 milliseconds. In reality, in addition to rewinding the cassette, you also need to find the necessary cassette in the storage, which is also a non-trivial task (see KDPV).
The latest LTO model has a tape scrolling speed during read / write about 15 km / h (4 m / s), and the heads are positioned with an accuracy of 3.2 nanometers.
The sequential read and write speeds to tape are faster than modern HDDs. In the latest generation LTO-9, read / write occurs in parallel on 32 tracks, and the speed reaches 400 megabytes per second per second uncompressed or 1 GB / s compressed.
Niches of use
Based on the advantages and disadvantages of the film, the options for its use are clear. They are reliable drives for cheap, long-term storage with good read / write speeds but no instant access. Thus, they are best suited for “cold” storage of backups.
In 2011, Google accidentally deleted mail in 40 thousand mailboxes… Backups on all servers suffered. The data could only be recovered from the tape. Then it turned out that Google also uses tape for backup, also like Microsoft and other cloud providers, not to mention their customers.
An unusual example of a long-term backup storage is GitHub Arctic World Archive on Svalbard. Moreover, it is cold storage both literally and figuratively. It is located at a depth of 250 meters in the permafrost and is designed for a thousand years of storage.
True, there is not a magnetic tape, but a photographic film with silver halides in polyester produced by the Norwegian company Piql. Such a film has a lifespan of at least 500 years.
One frame on film from a backup of the GitHub repositories, a source
The complete code of 100 million repositories in .tar took up 21 TB on 186 reels. Together with the archive, we put technical guides on QR decoding and formats so that our descendants can convert QR codes back into code and run it.
Cold storage rates are offered by Amazon and other cloud providers. Cold storage is much cheaper, but data retrieval is expensive. For example, in the service S3 Glacier Deep Archive storage 1 terabyte costs only $ 1 per month (12-48 hours access). In comparison, standard S3 storage is 23x more expensive.
Information in the global infrastructure snowballs as billions of new devices are connected. According to a recent study by IDC, the total storage capacity in the global global infrastructure will grow from 16 to 163 zettabytes over the period 2016-2025.
Now the number of ultra-large data centers in the world has reached 597… A special term is used for them: Hyperscale Data Center (HSDC). 52 similar structures were built last year.
Amazon, Microsoft and Google account for more than half of all large data centers.
Some modern scientific instruments generate such a huge amount of data that they cannot be stored except on tape drives. For example, the Large Hadron Collider generates 140 TB per day, and a giant distributed radio telescope SKA (Square Kilometer Array) with thousands of parabolic antennas will produce up to 1 exabyte per day… This is comparable to the volume of traffic on the entire global Internet (5.3 exabytes per day in 2020).
An artistic representation of the SKA antenna array. Picture: SPDO / TDP / DRAO / Swinburne Astronomy Productions
For such scientific instruments, the two most important parameters are high storage capacity and high write speed, and access time is no longer so important. Therefore, tape drives are used here.
By IBM assessmentToday, approximately 345,000 exabytes of data are stored on magnetic tape worldwide. It turns out that the film is currently the main accumulator of human civilization. And it is very likely that this situation will continue in the near future.
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