A matter of time

Once upon a time, backups were performed at night, when there were few or no users on the system and there was plenty of time and capacity. Nowadays, users are on systems around the clock, and there's no period when you can shut everything down for backup. As information sources explode and regulation increases, there's so much more to be backed up that we need ever more time and capacity to do so.

So we tell the backup software that it's writing to a tape drive, when in fact we're pointing it at a hard disk. You can think of a disk drive as a large, upfront cache that eliminates delays in changing tape reels or cartridges, or in repositioning tape media for noncontiguous data.

The virtual tape libraries emulate industry-standard-based physical tape drives and libraries, presenting themselves as tape to all of the common backup software applications. A backup media server sends backup streams to a virtual tape library, which writes the data sequentially -- that is, in native tape format -- to disk storage. Through this bit of hocus-pocus, the virtual tape library appears to the system as anoth-er automated tape library, but the fact that data is being written to disk means backup jobs are completed significantly faster, often by a factor of 10 or more.

Virtual systems emulate tape operations even to the point of assigning bar codes to virtual tape "reels" or "cartridges" used by the backup software.