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the I/O rate and highly sequential read operations for the MB/sec numbers. They also vary depending on the server type used.

The 2.8 GB/sec sequential read figure—and even significantly more—is achievable with a properly configured DS8300.

A properly configured DS8100 can reach read hit I/O rates with numbers in the 6 digits. The DS8300 does more than double that of the DS8100. These are rough estimates based on the technology and architectural possibilities, and are presented just to help you start imagining what might be possible. More precise figures cannot be stated without access to benchmark results or your own benchmark experience.

What we can expect to see is a significant improvement in response time and throughput with cache-hostile workloads due to the very fast Fibre Channel switched disk subsystems. A new caching algorithm, SARC, is used to guarantee a more efficient cache management than with the old LRU approach. This, in turn, will also positively contribute to better response times for all workloads which show pure locality of reference with the LRU approach.

12.5.3 Appropriate DS8000 size in z/OS environments

The potential of the architecture, its implementation and utilized technology allow for some projections at this point (though without having the hard figures at hand). Rules of thumb have the potential to be proven wrong. Therefore, you see here some recommendations on sizing which are rather conservative.

A fully configured ESS 800 Turbo with CKD volumes only and 16 FICON channels is good for the following:

￿Over 30,000 I/Os per second

￿More than 500 MB/sec aggregated sequential read throughput

￿About 350 MB/sec sequential write throughput mirrored in cache

Without discrete DS8000 benchmark figures, a sizing approach to follow could be to propose how many ESS 800s might be consolidated into a DS8000 model. From that you can derive the number of ESS 750s, ESS F20s, and ESS E20s which can collapse into a DS8000. The older ESS models have a known relationship to the ESS 800.

Further considerations are, for example, the connection technology used, like ESCON, FICON, or FICON Express channels, and the number of channels.

Generally speaking, a properly configured DS8100 has the potential to provide the same or better numbers than two ESS 800s. Since the ESS 800 has the performance capabilities of two ESS F20s, a properly configured DS8100 can replace four ESS F20s. As the DS8000 series scales linearly, a well configured DS8300 has the potential to have the same or better numbers concerning I/O rates, sequential bandwidth, and response time than two DS8100 or four ESS 800s. Since the ESS 800 has roughly the performance potential of two ESS F20s, a corresponding number of ESS F20s can be consolidated. This applies also to the ESS 750, which has a similar performance behavior to that of an ESS F20.

Based on customer workload data, an IBM internal modelling tool can project how many ESS 800s to configure and then consolidate the ESS 800s to respective DS8000 models.

Processor memory size considerations for z/OS environments

Processor memory or cache in the DS8000 contributes to very high I/O rates and helps to minimize I/O response time.

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