The HPSS component that manages tape mounts for modern tape libraries is the HPSS PVR (physical volume repository). HPSS streamlines the way cartridge move-requests are processed. Improved tape library efficiency delivers higher tape mounts per hour, which reduces time to first byte.
Library Efficiency
General PVR Improvements
The following features significantly raise the mount rate performance for all modern tape libraries that use the HPSS PVR:
- Expediting command processing by minimizing communications with the library before sending each command.
- Further reducing individual move request overhead by minimizing waits during retries.
- Allowing a single control path to queue up to 16 commands by implementing SCSI command queuing.
- Implementing a move scheduler to interlace tape mounts and tape dismounts so the robot is always holding a tape when moving.
The mount rate performance of the IBM TS4500 tape library climbed from 78% to 99% of the manufacturer’s mounts per hour. Before these software updates, HPSS performed 702 mounts per hour. After these updates, HPSS achieved 894 mounts per hour. The mount rate performance of the Spectra Logic tape library climbed from 42% to 80% of the manufacturer’s mount per hour exchange rate and required additional updates.
Spectra Logic PVR Improvements
The HPSS developers worked closely with the Spectra Logic team to implement the following features to maximize tape-handling efficiency of their tape libraries:
- Detection of Spectra Logic library zones so that both robot arms are kept busy.
- Detection of Spectra Logic TeraPack boundaries in the robot and grouping moves by TeraPack so that multiple cartridges can be mounted and dismounted with each TeraPack move.
Before these software updates, HPSS only reached 80% of the manufacturer’s mounts per hour. After these updates, HPSS achieved 99% of the manufacturer’s mounts per hour.