Disk backup is on the upswing, and the backup and archive market is looking more at low-cost disk arrays and remote archiving solutions to replace tape for the reason of higher performance and recent stories of lost tapes. But tape isn’t dead yet, at least according to some tape industry leaders. The party line among tape vendors is that disk backups are faster, but tape will survive for archiving.
Tape still has a cost advantage over disk. Even though disk prices per GB have been falling much faster than tape, tape is still cheaper on the whole. Tape has secondary advantages such as portability and high capacity. It’s also a well-proven technology, and that gives it a high comfort factor. In every other respect, the advantage lies with disk. Disks are much faster and it’s a lot easier to access and manage data stored on disks.
Despite vendors urging disk-only solutions, the trend isn’t so much to replace tape with disk as to supplement existing tape systems with disks that serve as partial backup. In some cases, this is a true disk-to-disk-to-tape system where the data is transferred to disk and immediately written to tape. In other cases, the disks handle the immediate backup and data is written to tape for long-term backup or archival storage.
Factoring in archival storage is important, because backup and archiving are not the same thing. The assumption in backup is that the data will only be maintained for a few days to a couple of months, and that therefore administrators will be dealing with a finite, manageable quantity of data. In archival storage, where data is kept for years, tape is still the superior solution, because it is cheaper, more durable over the long term and more portable.
However, most enterprise data doesn’t need to be archived. You need to archive material for several purposes: Regulatory or corporate policy requirements, data that doesn’t lose value over time (such as an oil company’s geological survey results) and data that is important historically or because it can be repurposed by something such as data mining. It isn’t unusual to need to save less than 10% of a company’s information for more than three months. By storing the data temporarily on disks, especially inexpensive iSCSI SATA disks, and only archiving data as necessary, companies can keep from outgrowing their existing tape libraries and drives.
In the end, the choice of tape, disk or disk-and-tape needs to be driven by your actual requirements and economic constraints. Don’t assume that one class of solutions is right for you.