Magnetic Tape Data Storage - Viability

Viability

For decades tape storage has offered cost and storage density advantages over many other storage technologies, such as disk storage. And for decades medium-sized and large-sized data centers have deployed both tape and disk storage to complement each other, with tape the favorite choice for tertiary and archival data storage. Storage technologies continue to advance both functionally and economically, and storage vendors compete aggressively against each other. Analysts are lining up on both sides of the "disk versus tape" argument.

The costs of disk storage have decreased faster than that of tapes. Until about the end of the twentieth century prices and capacities allowed backing up a desktop hard drive to tape, such as inexpensive Travan, much more cheaply and more compactly than backing up to an additional, external or removable, drive. Later drive prices dropped, drives with capacities of hundreds to a few thousands of megabytes started to be used on relatively inexpensive machines, and backing up to an external USB drive became cheaper, and the drive more compact, than tape for a non-networked machine used by a business or serious user.

As a basic comparison, mainframe-class tape drives, such as Oracle's Sun StorageTek T10000B, are priced at approximately US$37,000 each, excluding tape libraries. (IBM's TS1130 is also representative of this storage class.) At any single moment in time each T10000C tape drive can read and/or write to one tape cartridge which can contain up to 5TB of uncompressed data. Real-world sequential data transfer speeds are high (sustained 240MB/second for the T10000C and 160MB/second for the TS1130) compared to disk. However, PC-class hard disks are priced below $200 for about 3TB. One mainframe-class hard disk still has a much lower price than one mainframe-class tape drive, so the economics might favor disk.

However, the key difference is that tape drives can exchange their magnetic media (the cartridges) frequently, while the magnetic media installed inside each hard disk is fixed and cannot be swapped. (The drives themselves could be moved if installed in swappable caddies at extra cost, with extra cost hot-swappable infrastructure.) Mainframe-class tape drives are almost always installed in robotic tape libraries which are often quite large and can hold thousands of cartridges. The StorageTek SL8500 library is one representative example (and IBM also sells tape libraries). The smallest SL8500 library holds up to 1,448 tape cartridges, for 1.4 Petabytes of online uncompressed storage. An equivalent amount of PC-class hard disk storage would be priced at $100,000 or more for the drives. The tape library would likely deliver a higher sustained sequential write speed, the media would be more rugged (for off-site storage), the media would meet or exceed long-term archival storage requirements (for reliable retrieval decades into the future), and the data center power and cooling requirements would be considerably lower. The economics of this comparison are more complicated than a single-spindle versus tape drive comparison.

Whether tape's characteristics versus disk are useful or not will depend on the particular data center and its data storage requirements. What has tended to happen in recent years is that the amount of data has grown exponentially, with both disk (especially) and tape participating in the growth. In the early twentyfirst century solid state storage encroached on disk's previous near-monopoly in random access non-volatile data storage, while disk pushed into tape's territory to some extent, particularly in situations where sequential data access is only a relatively small part of a particular data center's storage requirements.