The most common physical tape operations are backup, Hierarchical Storage Management (HSM) migration, data archiving, batch processing and work tapes that are used for temporary staging, Syncsort work files, transaction log files, and other tasks. Media management is one challenge of the tape environment; it requires planning, and tape management tasks consume IT staff time.
To make maximum use of the tape media, many data sets are stacked onto a single physical tape. When tape space utilization is low, a recycle operation (similar to a disk defragmentation program) is performed. Once a certain percentage of the files on a tape are scratched, HSM can perform a tape recycle. This involves purging the scratched data and combining current data with other tapes involved in the recycle to create a new physical tape. This process is designed to minimize the wasted sections of tape and optimize media utilization.
With physical tape, the recycle process involves multiple tape drives; if some of the drives are in use in other processes, the recycle task must wait until those drives are free. This tape drive contention slows down the recycle process. In addition, reading the tape can take a long time. Together, these issues can result in recycles taking longer than the window allotted, creating delays and contention problems across the environment.
When using virtual tape servers, HSM recycles involve additional complexity, since both the physical and the logical tape files must be included. With virtual tape servers, HSM data sets are written to cache (the logical volume), and multiple data sets are then stacked and written out to tape (the physical volume). In this scenario, the recycle process must be executed twice—once to the physical tape infrastructure and once to the logical HSM file—which potentially doubles the tape drive contention as well as the delays associated with reading from tapes.
On the other hand, a disk-based virtual tape solution can be much more efficient and effective. First, because no physical tape is used, there are no actual tape mounts, robotic activity, or tape rewinds to deal with. Data is all stored on disk, so no tape drive contention issues arise, and there are no constraints for the number of tape drives available to mount the VOLSERs during the recycle process. Disk is significantly more reliable and can provide extremely fast throughput—
gigabytes per second—speeding the recycle and enabling completion within the allotted time. It offers greater flexibility as well; the virtual cartridge size is configurable, so you can set a size based on your specific needs. In addition, there’s no “double duty” recycle process as is required with virtual tape servers (and outlined previously).
While physical tape has long been a staple of mainframe data centers, today’s disk-based “tape” technologies offer significant improvements for tape tasks such as tape recycles. The speed and ease-of-use of a disk-based virtual tape solution can greatly improve productivity and reduce the number, time, and complexity of IT tasks.