IBM DS8000 manual Performance, Sequential Prefetching in Adaptive Replacement Cache Sarc

offer the most value to the customers. On the list of possible applications are, for example, Backup/Recovery applications (TSM, Legato, Veritas, and so on).

1.4 Performance

The IBM TotalStorage DS8000 offers optimally balanced performance, which is up to six times the throughput of the Enterprise Storage Server Model 800. This is possible because the DS8000 incorporates many performance enhancements, like the dual-clustered POWER5 servers, new four-port 2 GB Fibre Channel/FICON host adapters, new Fibre Channel disk drives, and the high-bandwidth, fault-tolerant internal interconnections.

With all these new components, the DS8000 is positioned at the top of the high performance category.

1.4.1 Sequential Prefetching in Adaptive Replacement Cache (SARC)

Another performance enhancer is the new self-learning cache algorithm. The DS8000 series caching technology improves cache efficiency and enhances cache hit ratios. The patent-pending algorithm used in the DS8000 series and the DS6000 series is called Sequential Prefetching in Adaptive Replacement Cache (SARC).

SARC provides the following:

￿Sophisticated, patented algorithms to determine what data should be stored in cache based upon the recent access and frequency needs of the hosts

￿Pre-fetching, which anticipates data prior to a host request and loads it into cache

￿Self-Learning algorithms to adaptively and dynamically learn what data should be stored in cache based upon the frequency needs of the hosts

1.4.2IBM TotalStorage Multipath Subsystem Device Driver (SDD)

SDD is a pseudo device driver on the host system designed to support the multipath configuration environments in IBM products. It provides load balancing and enhanced data availability capability. By distributing the I/O workload over multiple active paths, SDD provides dynamic load balancing and eliminates data-flow bottlenecks. SDD also helps eliminate a potential single point of failure by automatically re-routing I/O operations when a path failure occurs.

SDD is provided with the DS8000 series at no additional charge. Fibre Channel (SCSI-FCP) attachment configurations are supported in the AIX, HP-UX, Linux, Microsoft® Windows, Novell NetWare, and Sun Solaris environments.

1.4.3 Performance for zSeries

The DS8000 series supports the following IBM performance innovations for zSeries environments:

￿FICON extends the ability of the DS8000 series system to deliver high bandwidth potential to the logical volumes needing it, when they need it. Older technologies are limited by the bandwidth of a single disk drive or a single ESCON channel, but FICON, working together with other DS8000 series functions, provides a high-speed pipe supporting a multiplexed operation.

￿Parallel Access Volumes (PAV) enable a single zSeries server to simultaneously process multiple I/O operations to the same logical volume, which can help to significantly

14DS8000 Series: Concepts and Architecture