Hitachi 9900 manual Hitachi Data Systems, Read-aheadfor High-performanceSequential Reads

Hitachi Data Systems

The CSW is at the heart of the Lightning 9900 V Series.

The Cache Switch Provides Non-blocking Switched Access to Cache

At the heart of the Lightning 9900 V Series are four Cache Switches (CSWs). Together, these four switches (in the Lightning 9980V ™ system) use a parallel switch fabric bus (PSFB). The CSW is a specially designed crossbar switch that functions as a combination MUX, path arbitrator, and non-blocking network switch. The CSW functions as a MUX by supporting eight paths into the processor side of each switch and eight paths to the cache modules. All total, there are 32 paths at the processor side of the fabric network and 32 paths to the cache modules from the cache side of the fabric network.

The Lightning 9980V System Provides 64GB of Fully Addressable Cache

The Lightning 9980V system supports up to 64GB of data cache, all directly addressable. Separate cache modules (up to 3.0GB) are used for control storage. Competitive systems use their cache for both data and control information, limiting the amount of usable data cache and creating performance limitations for certain workloads.

Advanced Cache Algorithms of the Lightning 9900 V Series

The Lightning 9900 V Series has a variety of advanced cache algorithms and software solutions that provide exceptional performance.

A portion of cache memory can be allocated to specific data.

Hitachi FlashAccess™ Software Allows Data Sets to be Permanently Placed in Cache

Hitachi FlashAccess software allows users to dynamically “lock and unlock” data into cache in real time. Read and write functions are then performed at cache speeds, with no disk latency delay. FlashAccess software, a portion of cache memory can be allocated to specific data. Administrators can add, delete, or change FlashAccess software managed data at any time, quickly and easily.

In IBM® S/390® environments defined by the Logical Volume Image (LVI), cache data can be as small as a single track or as large as a full 3390. For increased configuration flexibility, FlashAccess software offers multiple modes of operation. It can be used in conjunction with Hitachi RapidXchange™ software to increase the speed of data transfer and, therefore, improve performance of mainframes to open systems data exchange. RapidXchange software supports both open-to-S/390 and open-to-open high-speed data transfers.

Read-ahead for High-performance Sequential Reads

Read clustering in the Lightning 9900 V Series is enabled using built-in heuristics to read ahead for every I/O. The heuristics are applied to determine if the data is being accessed sequentially. If so, then the Lightning 9900 V Series reads ahead pages corresponding to that data. Read-ahead helps to ensure that when a client read request is received the requested data will already be stored in the data cache, so the request can be satisfied immediately.

Control Memory Hierarchical Star Network

The second component of the Hi-Star architecture is the Control Memory Hierarchical Star Network (CM-HSN). This is a point-to-point network that handles the exchange of control information between the processors and control memory. The control memory contains information about the status, location, and configuration of the cache, the data in the cache, and the configuration of the Lightning 9900 V Series system (as well as other information related to the operational state of the system). Two control memory areas are

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