Product manual

CDA 7 5630 Product Manual
G-2 77 A1 69UP Rev00
B
Backplane
Card that accommodates the director, cache, and adapter cards.
Bit
The smallest unit of computer memory. A bit can hold a value of 0 or 1.
Byte
Term that indicates an 8-bit hexadecimal construction.
C
Cache
Random access electronic storage used to retain frequently used data for faster access by the
channel.
Cache Slot
Unit of cache equivalent to one track.
Channel Director
The component in the Symmetrix subsystem that interfaces between the host channels and data
storage. It transfers data between the channel and cache.
Command Descriptor Block (CDB)
The structure used to communicate commands from an initiator to a target. This structure may be 6
bytes, 10 bytes, or 12 bytes in size.
D
Data Availability
Access to any and all user data by the application.
Delayed Fast Write
There is no room in cache for the data presented by the write operation. Therefore, the write is
delayed until there is room in cache.
Destage
The asynchronous write of new or updated data from cache to disk device. See also the term
"Stage".
Device
A uniquely addressable part of the Symmetrix subsystem that consists of a set of access arms, the
associated disk surfaces, and the electronic circuitry required to locate, read, and write data. See
also Volume.
Device Number
The value that logically identifies a disk device in a string.