Wait a moment — have I stepped into a time machine? We all know that magnetic tape is so….yesterday. Isn’t all storage these days on solid-state or hard-disk drive (HDD) memory?
The answer is yes, it is; and no, it isn’t. A recent article in The Wall Street Journal , “Companies Look to an Old Technology to Protect Against New Threats” noted that companies are once again storing data on tape, just in case. This isn’t just an anecdotal trend, either: there are some solid numbers showing increases in shipments of tape units, as well as the amount of data being stored on tape.
While tape is not as easy-access as solid-state or HDD memory, that attribute is also one of its virtues, as it functions as a robust, slower-time, recovery mechanism should the “worst” happen. Further, since the tape is not “on line,” it is much less accessible to hackers. The Wall Street Journal article notes that “the federal government, financial-services firms, health insurers and other regulated industries still keep tape as a backup to digital records. Now a range of other companies are returning to tape as hackers get smarter about penetrating defenses.”
If you think of tape in terms of those old-fashioned large reel-to-reel units, those are long gone, except for archival reels which may be lucky to find a playback deck. The tape industry standardized on easy-to-handle cartridges which can be retrieved and returned via robotic arms, Figure 1 , often configured in large arrays of tape-drive “farms.” There are even standards which define form factor, formats, and more, assisted by the Tape Storage Council, a collaborative industry group founded in 2012 to promote the use and technology innovations occurring within the tape-storage industry.
This LTO-7 tape drive from Quantum Corp. features backup-and-restore performance at speeds up to 750 MB/sec (2.7 TB/hr) and can support 15TB of data on each cartridge (Source: Quantum Corp.)
Two key standards are the Linear Tape File System (LTFS) , which allows the tape to be used almost like a hard disk drive (the key word here is “almost”), and Linear Tape-Open (LTO) , developed in the late 1990s as an open standards alternative to the proprietary magnetic tape formats that were available at the time. Their recent report “Technology Advances Propel Tape to New Markets” is a brief and highly readable summary of the state of the art and applications.
The argument for tape versus solid-state or HDD is not just based on security. The Tape Storage Council claims it is also an issue of reliability and bit error rate (BER), Figure 2 , claiming one error per 1019 bits for LTO-7 versus one error in 1016 bits for top-rated HDDs (details on an LTO-7 from Quantum Corp are here). That’s an impressive difference of three orders of magnitude. Other performance comparisons between tape and HDD are also noteworthy and may break old myths, their report notes with some interesting numbers (yes, they are biased, but it is still an interesting read.)
This comparison of various data-storage media shows that high-performance tape offers the lowest bit error rate of different technologies, by a factor of 1000. (Source: Tape Storage Council)
So, what’s all this have to do with “analog?” It’s simple: a tape system is a miniature analog-signal, wireless-transmission link, even if the data is digital. In many ways, it is similar to an RF channel, except that the RF has been replaced by magnetic fields as the energy conveyance. There are issues of jitter, SNR, intersymbol interference, varying signal strength – all the issues that affect RF “wireless” links.
Of course, the read-channel begins with an analog preamplifier, mounted as close as possible to the read head itself, and a variable-gain amplifier (VGA). But that’s only the beginning of the analog signal processing, as advanced tape systems use a read channel with partial response, maximum likelihood (PRML) signal-detection circuitry to maximize chances for successful, and error-free data recovery despite channel irregularities. While the physical scale may be far less than an RF link, the signal-path blocks are similar (see “Computer Peripherals, Chapter 9”).
There’s a large element of “back to the future” irony here. Not only was magnetic tape the first high-density data-storage mechanism, predating hard disk drives, but early “hobbyist” personal computers used the consumer-audio Philips cassette as a low-cost medium (admittedly low speed, low capacity) for both loading the operating system via a “boot loader” and also storing programs and data. Use of magnetic tape for both hobby and commercial applications fell out of favor with the development of reasonably priced, random-access, high-density hard drives, but the underlying magnetic-tape technologies still have a vital role to play – one which seems to be growing again.
It’s the old story: where technologies are involved, “never say never” to what seems to be an obsolete technology. In a new guise or iteration, it may become quite viable and attractive again, and be a solution to new problems.
Have you used a leading-edge, LTO/LTFS tape drive? Did you ever use a cassette drive way back in the day?