Filter
Top Products
Hitachi Lightning 9900™ User and Reference Guide 29
Chapter 3 Functional and Operational Characteristics
3.1 New 9900 Features and Capabilities
The Hitachi Lightning 9900™ subsystem offers the following new or improved features and
capabilities which distinguish the 9900 subsystem from the 7700E subsystem:
Support for FICON™ channel interface.
Sixteen (16) logical control unit (CU) images.
State-of-the-art hard disk drives of 18-GB, 47-GB, 73-GB, 146-GB, and 180-GB capacities.
Up to 32 GB cache memory for the 9960 subsystem and 16 GB cache for the 9910.
Up to 32 host interface ports [ExSA™ (ESCON
®
) and/or fibre-channel].
Up to 16 host interface ports (FICON™).
Up to 256 logical paths per ExSA™ (ESCON
®
) channel interface.
Up to 512 logical paths per FICON™ channel interface.
Up to 4096 device addresses.
Prioritized port control for open-system users.
3.2 I/O Operations
The 9900 I/O operations are classified into three types based on cache usage:
Read hit: For a read I/O, when the requested data is already in cache, the operation is
classified as a read hit. The CHIP searches the cache directory, determines that the data
is in cache, and immediately transfers the data to the host at the channel transfer rate.
Read miss: For a read I/O, when the requested data is not currently in cache, the
operation is classified as a read miss. The CHIP searches the cache directory, determines
that the data is not in cache, disconnects from the host, creates space in cache, updates
the cache directory, and requests the data from the appropriate ACP pair. The ACP pair
stages the appropriate amount of data into cache, depending on the type of read I/O
(e.g., sequential).
Fast write: All write I/Os to the 9900 subsystem are fast writes, because all write data
is written to cache before being destaged to disk. The data is stored in two cache
locations on separate power boundaries in the nonvolatile duplex cache (see section
2.2.3). As soon as the write I/O has been written to cache, the 9900 subsystem notifies
the host that the I/O operation is complete, and then destages the data to disk.