Transparency to the backup application

Because there is a significant performance increase when writing data to disk, using virtual tape libraries reduces the amount of time that it takes to backup the data.

Virtual tape libraries

Like their physical counterparts, virtual tape libraries have cartridge slots, one or more tape drives, an import/export slot, and even a robotic arm. These attributes (number of slots, capacity of tape drives, and so on) are defined by type. The NearStore VTL comes with a number of predefined virtual library types. You can also create new types to fit your needs.

Virtual tape drives

Like virtual tape libraries, the characteristics of virtual tape drives are defined by type. This includes vendor information, the capacity of the drive, and tape optimization algorithm.

Virtual tapes

Virtual tapes are the NearStore VTL equivalent of physical tapes. Like physical tapes, virtual tapes have a specified capacity and are labeled by barcodes. Backup applications use these barcodes to track virtual tapes in the same way that they track physical tapes. In fact, there is a one-to-one correspondence between virtual and physical volumes.

Import/Export

When you import a physical tape, the NearStore VTL creates a virtual tape that is the exact copy of that physical tape, including barcode and file mark information. Likewise, when you export a virtual tape, the NearStore VTL sends the data from the virtual tape to an attached physical tape device, resulting in a physical copy of the virtual tape. You can also use the cloning feature of the backup application as a slower alternative. The tapes that the NearStore VTL creates are in the native format of the backup application.

Tape optimization

All data is compressible at a different rate. This means that each time you back up data to physical tape, the actual amount of data that the physical tape drive writes to tape depends on the compressibility of the data. Because the NearStore VTL must be able to export virtual tapes to physical tape, it is crucial that the amount of data on the virtual tape can fit on the physical tape, without going over its capacity. If the data from a virtual tape cannot fit on a physical tape, you cannot export or clone it.

Most VTL vendors solve this issue by matching the capacity of any virtual tapes to the native (uncompressed) capacity of the corresponding physical tapes. This is not really a solution, because it does not take compression into account. For example, if the physical tape drive can compress the data at a ratio of 2:1, over half of the physical tape would not be used when you exported the virtual tape.

The NearStore VTL addresses the compression issue by monitoring the compressibility of each data stream and dynamically adjusting the size of the virtual tape to closely match the compressed capacity of the corresponding physical tape. Because the NearStore VTL does not store compressed data when using tape optimization, there is no performance impact.

Ease of use

Because the NearStore VTL virtual tape libraries function in much the same way as physical tape libraries (including the way that they are displayed to backup applications), you do not have to alter the existing backup and restore. This means that you can back the up data to disk using the existing infrastructure and work procedures.