This article can also be found in the Premium Editorial Download "Storage magazine: Tools for successful data migrations."
Download it now to read this article plus other related content.
What virtualization buys
Virtualizing tape devices allows host apps to access a logical tape drive while a virtual appliance accesses actual physical tape drives. The biggest bottleneck in disk-to-tape operations is writing data to tape; virtualization at this level lets logical mounts be presented to the host whether or not physical tape drives are available. Virtual solutions gather tape data from the disk cache and later write the data to tape, as mainframe tape management systems have done for years.
|Shortcomings of automated tape libraries|
Automated tape libraries (ATLs) lack a common control standard. Each manufacturer provides its own set of commands and protocols. Although ATLs can hold drives that support multiple connectivity types (e.g., Fibre Channel and FICON), they don't expose their unique command sets to a common interface or API set. Even backup software providers have difficulty recertifying their functionality with each library iteration.
With the robot as the control point, only one OS host can have access to a tape drive at a time. The host is typically running backup software that contains a catalog with configuration information. This host system becomes a logical single point of control, forcing any other host that wants access to the ATL to go through it for communication. There are ways to circumvent this monopolistic control with software like StorageTek's (now owned by Sun) Automated Cartridge System Library Software (ACSLS), which provides some ability to arbitrate control away from the backup software, but only between common hosts.
Tape vendors can help open their products by creating a standard set of ATL commands, moving more intelligence to the library using meta data about what's stored in the library, and by exposing robot control software like ACSLS with API extensions that can be manipulated and invoked by other software products, including the competition's. That, at least, would be a start.
Another shortcoming is that duplicate virtual appliances are needed at the DR site to recover data, and these devices are typically pricey. They may also require purchasing backup software upgrades. For example, Veritas charges by the number of tape drives (real or virtual) needed, so a 40-drive virtual environment at $3,000 per drive would cost $120,000. Veritas also adds $2,000 for a SAN-shared drive. If the 40 virtual drives were shared, the total cost would be $200,000.
Jeff Hackling, VP of systems support at Global Payments Inc. in Atlanta, runs a data center with almost every major host type--mainframe, Unix, Windows, AS/400 and Tandem. "Thus far, Global has not pursued tape resource sharing," Hackling says. But, he adds, "as our open-systems data storage has significantly increased recently--from 2TB to 25TB--we may need to look at tape sharing."
This was first published in November 2005