Product manual

Glossary
77 A1 69UP Rev00 G-3
Diagnostics
System level tests or firmware designed to inspect, detect, and correct failing components. These
tests are comprehensive and self-invoking.
Differential Interface
An electrical signal configuration that uses a pair of lines for transfer. This configuration (as
compared to a single-ended interface) has a higher tolerance for common-mode noise and little
crosstalk when used with twisted pair cables. It supports cables lengths to 25 meters (82 feet). See
also Single-ended Interface.
Directors
The components in the Symmetrix subsystem that allows Symmetrix to transfer data between the
host channels and disk devices. See also Channel Director and Disk Director.
Disk Director
The component in the Symmetrix subsystem that interfaces between cache and the disk devices.
DMA
Direct Memory Access.
Dual-Initiator
A Symmetrix feature that automatically creates a backup data path to the disk devices serviced
directly by a disk director, if that disk director or the disk management hardware for those devices
fails.
Dynamic Path Reconnect (DPR)
A function that allows disconnected I/O operations with Symmetrix to reconnect over any available
channel path rather than be limited to the one on which the I/O operation was started.
Dynamic Sparing
A Symmetrix feature that automatically transfers data from a failing disk device to an available
spare disk device without affecting data availability. This feature supports all devices in the
Symmetrix subsystem and is used with the Mirroring and SRDF options.
E
EPO
Emergency Power Off.
Error Verification
The process of reading, checking the error correction bits, and writing corrected data back to the
source.
ESP
Enterprise Storage Platform. Symmetrix ESP is a functional enhancement that allows simultaneous
storage and access of mainframe data and open systems data on the same Symmetrix 53xx system.