HPSS is considered best of breed for tape because of our efficient use of tape hardware and media. Tape hardware and media efficiency translates to a lower total cost of ownership (TCO) of long term data storage. HPSS increases hardware and media efficiency by maximizing tape transfer performance, reducing wasted movement of tape media and tape robotics, cutting the cost of redundant tape, and protecting against silent data corruption on tape.
Best of Breed for Tape
HPSS maximizes tape transfer performance
Most clustered file systems and high performance computers can perform I/O at many gigabytes per second, while modern tape drives have native transfer rates less than 500 MB/s. HPSS can be configured to transfer a single file in parallel to multiple tape drives. This allows HPSS to transfer large files at speeds far beyond the limits of a single tape drive. In 2017, Oak Ridge National Laboratory (ORNL) deployed a 4-wide tape stripe into production and are logging single file transfer rates that exceed 1 GB/s using 252 MB/s tape technology.
Small File Tape Aggregation
Writing small files to tape is often an arduous task, but NOT for HPSS. The HPSS tar utility (HTAR) can be used to store small files in an efficient manner. Without HTAR, HPSS can be configured to automatically group small files on tape to improve tape transfers. HPSS can often achieve near-native tape transfer rates even when doing tape I/O with the smaller files.
HPSS reduces wasted movement of tape media and tape robotics
Efficient use of tape media
HPSS groups tape recall requests by tape cartridge to reduces unnecessary tape mounts and dismounts. HPSS performs offset ordered tape recalls when using LTO tapes. Offset ordered tape recalls improve the efficiency of recalling collocated files. Modern tape drives write data to tape in a serpentine manner, writing data in different directions on alternating wraps. Because of the serpentine nature of data on tape, LTO tape offset ordering does not minimize seek-times for files that are not collocated.
HPSS performs recommended access ordered (RAO) tape recalls when using enterprise tapes. RAO is an enterprise tape drive feature. HPSS sends a request to the enterprise tape drive, and the tape drive efficiently orders the recalls for HPSS. RAO improves the seek-time between files on tape by 40% to 60%. When requirements demand high tape recall rates, RAO and enterprise tape are often the most economical long term storage option at scale.
Efficient use of tape robotics
HPSS exploits dual active tape robot movement for tape libraries supporting this capability. Lee Jesionowski, IBM’s tape automation lead architect says, “This can more than double the tape mount rate efficiency.” HPSS also orders tape mount requests to ensure the tape robot is not moving great distances without a cartridge in the gripper.
HPSS versions 7.5.2 and 7.5.3 have introduced SCSI PVR and Spectra Logic library compatibility improvements that have increased tape mount rate efficiency from 78% to 99% on IBM tape libraries and from 42% to 99% on Spectra Logic tape libraries.
HPSS cuts redundant tape costs
Prior to the commercialization of RAIT, redundant tape was accomplished by making multiple tape copies. HPSS redundant array of independent tape (HPSS RAIT) is tape striping with one or more rotating parity blocks. HPSS has introduced a feature that cuts the cost of redundant tape by 50%, 66%, 75%, or more. In addition to reducing the cost of redundant tape, HPSS RAIT users enjoy all the benefits of striped tape – high speed tape reads and tape writes.
To further clarify the Oak Ridge National Laboratory (ORNL) 4-wide tape stripe cited earlier, it is a 4+Parity HPSS RAIT stripe, which also cut their projected dual-copy redundant tape cartridge costs by almost 75%.
HPSS protects against silent data corruption on tape
All data can be corrupted – data in motion and data at rest. Silent data corruption is when data corruption goes undetected. HPSS validates the integrity of data when data are written to tape using file checksums and T10 Logical Block Protection (T10 LBP). With HPSS end-to-end data integrity, corrupted data will not be written to tape. HPSS also provides a highly efficient data re-validation tool to validate data on tape. When data corruption is identified, redundant tape (multi-copy or RAIT) is used to correct the problem.