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 set when the virtual library is created. The NearStore VTL comes with a number of predefined library and virtual tape drive types. You can also create new library types to fit your needs.

Virtual tape drives

The NearStore VTL includes a number of virtual tape drive types. The type specifies such properties as 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 barcodes.

Control of physical library entry/exit port (EEP)

The correspondence between virtual tape movement and physical tape movement even extends to the movement of tapes into and out of libraries. When you move a virtual tape, that has a corresponding physical tape, to the virtual library entry/exit port, the NearStore VTL can move the physical tape to the physical library EEP. (This is controlled by the Move Physical Tapes to EEP After Virtual Export option.)

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.

Shadow tape pool and shadow tapes

When you export a virtual tape, in parallel with the creation of the physical tape, the NearStore VTL can create a shadow tape stored in the shadow tape pool. The backup application continues to manage the physical tape, with the shadow tape invisible to the backup application (and invisible to the library on the NearStore VTL). If you later import the physical tape, the NearStore VTL immediately moves the shadow tape to the library, which makes it available for reading while the physical tape is still being read. You can also manually import a shadow tape back to a virtual library.

Smart sizing

All data is compressible at different rates. 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 an efficient 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 remain unused 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.

Data compression

Smart sizing adjusts the size of a virtual tape to match the capacity of a physical tape by taking in account the physical tape drives own data compression algorithm. But a NearStore VTL can also use data compression to reduce the size of the data stored on a virtual tape. A NearStore VTL implements software-based data compression. Because software compression can increase capacity, but can significantly reduce data throughput, data compression can be separately enabled or disabled for each virtual tape (the default, data compression on or off, can be set separately for each virtual library when the library is created).

Ease of use

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