The evolution of backing up to tape and where it stands
Tape backup continues to have a cost advantage over disk, and there are still some use cases where the medium makes sense and will do so for the foreseeable future.
Tape has been around a long time -- if you count punched paper tape, it goes back to the 18th century, when it held instructions for automated looms. Most paper tape and magnetic wire and tape formats used in computing originated in music and video recording technology, from music boxes to cassette tapes used in early home computing systems to VCRs.
In the second half of the 20th century, most servers and other critical PC-based systems were backing up to tape, and most experienced system administrators had dealt with backups that failed to restore properly from tape. There were many reasons for this. Tapes were often stored improperly and used too many times. They were used in rotation and even left in the tape drive and overwritten every night for months or years.
No wonder they failed.
Miscommunication could happen between backup software and the tape drive, and restoring could require inserting and running a restore from several different tapes to get an incremental backup to work.
Most administrators were quite relieved to move on from tape to disk-based backups. Yet, organizations are still backing up to tape and using the medium for other procedures. Companies such as IBM, Quantum and Spectra Logic continue to develop tape drives and libraries and innovate with new tape formats and other new technology.
So, why is tape still around?
One of tape's key benefits is cost. A 15 TB LTO-7 tape costs approximately $100, while two 8 TB bare hard drives will cost several times that. If you look at the total cost of a 15 PB tape library versus a 15 PB disk-based backup system, the cost advantage of tape is even greater. The larger the data set, the greater the advantage for tape. A 10 TB disk-based backup system won't break the bank, but hundreds of petabytes is another story.
There will always be a place for backing up to tape, as long as costs are lower than the equivalent hard disk and flash-based systems.
There are areas where disk-based systems have an advantage over backing up to tape. Random access, used when restoring a file that a user has accidentally deleted, is faster with a disk system because with tape, the specific cartridge must be located, loaded into a drive and then moved to the point where the file is located. With tape it can take minutes or even hours to restore a file, compared with a couple of seconds for a disk-based system. Some tape systems address this by using a relatively small disk-based system to store a few days of backups.
The other side of this equation is streaming, or sequential, data, which is ideal for tape. This includes audio and video files that are large and sequential. Many special effects houses store the working files for their many versions of scenes on tape, for instance. Full backups that restore all the data, rather than one or two files, are also a better use of backing up to tape.
Another issue for some companies is off-site archiving. While cloud archiving is surging in popularity, some industries still have legal or corporate requirements to archive data off-site in a secure location. This is easier with tapes than hard drive-based systems, though if the data is meant to be recoverable rather than just meeting legal requirements, the tapes should be rotated back to the data center every five to 10 years to be rewritten onto new tape.
So, while the markets are smaller, and tape vendors continue to battle with ever-cheaper cloud archiving for market share, there will always be a place for backing up to tape, as long as costs are lower than the equivalent hard disk and flash-based systems.
