Introduction

The IBM TS7700 family is the latest in the line of tape virtualization products for the IBM Z platform. It is a highly scalable, reliable and high performing tape solution supporting today’s demanding IT environments.

The first generation of the TS7700 family (TS7740) was made available in 2006, nearly 10 years after the first IBM virtual tape server’s inception. For over 20 years the VTS and now TS7700 family has continued to evolve. The IBM TS7760 is the latest model of the family which became generally available in June 2016. TS7760 adopts IBM POWER8 technology, making it the most powerful and reliable model.

The IBM virtual tape servers have supported data compression for nearly two decades and now it’s getting better. Utilizing modern enhancements in compression technologies, the TS7700 4.1.2 release supports two additional compression options, providing its users with improved compressions, higher performance and a lower cost of ownership.

TS7700 Enhanced Compression – Background

The IBM TS7700 family has supported a form of ALDC compression ("standard" compression option) for data written to virtual tapes since the late 1990s. The compression engine has always been embedded within an ASIC on the IBM’s proprietary ESCON and now FICON adapter cards within the virtual tape server. It is very fast and demands minimal resources of the TS7700. Unfortunately, the algorithm has not changed since its adoption and its resulting compression ratios often can’t compete with modern industry wide alternatives. Higher compression ratios are expected for virtual tape application workloads.

One alternative allowing IBM Z customers to achieve a higher compression ratio is IBM Z Data Compression (a.k.a., zEDC) which is available on IBM zEnterprise EC12/BC12, IBM z13 and IBM z14. It too is fast, requires minimal resources and also results in very impressive compression ratios. However, zEDC does not yet support all tape applications and use cases, leaving an opportunity where users can still benefit from outboard TS7700 compression.

The TS7700 development team considered various options and concluded that with incredible improvements in firmware based compression algorithms, leveraging the performance of the TS7700’s embedded IBM POWER8 CPU was the best approach. There are three major benefits of using TS7700 firmware based algorithms.

  1. No additional hardware required – It is a firmware only implementation. No additional hardware is required and client’s investment in their TS7700 is retained with no additional cost.
  2. Time to market – A firmware based implementation requires less time to implement than an ASIC or FPGA based one. This drastically improves the time required for IBM to provide innovative enhancements and future improvements to the compression algorithms.
  3. Compression won’t grow stagnant – IBM and its clients benefit from the industries ever evolving compression algorithms. As existing algorithms improve and new ones blossom, the TS7700 can more easily adopt them.

The potential downside, is excessive CPU utilization and performance degradation. However, the IBM team discovered that CPU overhead can be minimal and performance usually improves significantly when compared to the standard compression algorithm. Different algorithms also utilize less CPU in exchange for smaller improvements in compressibility, which is why IBM chose two new options for the TS7700.

New TS7700 Enhanced Compression Options – "LZ4" and "ZSTD"

The TS7700 has added two firmware based compression algorithms. The industry standard LZ4, which is exceptionally fast and the industry standard ZSTD, which provides incredible compression.

Using the DATACLASS construct of DFSMS, users can choose which compression algorithm is applied for any given workload. A common logical device range, logical volume range and scratch pool can be used for all workloads. The assigned DATACLASS is used to determine which compression algorithm is applied for a new output tape. Using the z/OS Automatic Class Selection routines, users can assign an appropriate DATACLASS giving them the flexibility of workload assigned policies that only the IBM TS7700 can offer.

The following three compression algorithms are now available in the TS7700 R4.1.2 and later code.

  1. FICON Compression – Compression that is performed by the FICON adapter hardware within the TS7700 (supported for nearly two decades).
  2. LZ4 Compression (NEW) – Firmware based compression using the industry standard LZ4 Fast algorithm. This compression method is fast, uses minimal TS7700 CPU and provides improved compression over the standard FICON compression.
  3. ZTSD Compression (NEW) – Firmware based compression using the industry standard ZSTD algorithm. This compression method incurs slightly more overhead when compared to LZ4, but can result in much higher compression ratios.

Compression Ratio and Performance Achieved Using LZ4 and ZSTD

Overall, the compression ratio and performance has improved in the vast majority of use cases. IBM utilized a series of 18 IBM Z workloads which were similarly used in previous IBM zEDC tests. A summary of the results are as follows.

  • Compression Ratio

    • LZ4 outperformed the standard FICON in 16 of 18 test patterns. For the 16 cases which improved, it changed from +4% to +90%, with an average increase of +32%.
    • ZSTD outperformed the standard FICON compression in all 18 test patterns. The improvements ranged from +33% to +179%, with an average increase of +105%, that’s a 2x increase!
  • Performance

    • With improved compression, the resulting reduction of data means faster I/O operations within the TS7700. Less data to save to disk cache, less data moving to back end physical tape and less data replicating across grid links. This results in overall faster performance and its an attractive trade off for the additional TS7700 CPU consumption used by the firmware algorithms. In a 16Gb FICON configuration, standard FICON compression with 32KB blocks peaks around 3.8GB/s while ZSTD and LZ4 can reach 4.1GB/s channel speeds. When larger tape blocks are used, speeds can reach as high as 5GB/s using the new algorithms.

As you can see, the LZ4 and ZSTD compression options are very attractive additions to the IBM TS7700 family. To learn more about performance results under different use cases, please refer to the "TS7700 4.1.2 performance white paper". For more information on the new compression options and how to use them, please refer to the "IBM TS7700 Release 4.1 and 4.1.2 Guide".


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