
drawer
. A removable direct-access storage unit which
is installed in a frame. A drawer consists of disk drive
modules.
E
effective data rate
. The rate at which data can be
moved over a number of I/O operations. The effective
data rate depends on several factors such as the
distance between a channel and a control unit, the
specific control units and devices attached, the channel
programs used, and the amount of data moved.
ECC (Error Checking and Recording)
. Code bytes,
which are used for detecting and correcting read error.
These code bytes are added to each area of the record
whenever a record is written.
Enterprise Systems Connections (ESCON)
. A set of
IBM products and services that provide a dynamically
connected environment within an enterprise.
environmental-data
. Data the control unit must report
to the host; the data can be service information
message (SIM) sense data, logging mode sense data,
an error condition that prevents completion of an
asynchronous operation, or a statistical counter
overflow. The control unit reports the appropriate
condition as unit check status to the host during a
channel initiated selection. Sense byte 2, bit 3
(environmental-data present) is set to 1.
Environmental Record Editing and Printing (EREP)
Program
. The program that formats and prepares
reports from the data contained in the error recording
data set (ERDS).
erase
. To remove data from a data medium, leaving
the medium available for recording new data.
error recording data set (ERDS)
. The area in which
error records are logged. ERDS information is stored in
SYS1.LOGREC by MVS, in SYSREC by VSE, and in
the error recording area by VM.
extended count-key-data (ECKD)
. A set of channel
commands that use the CKD track format. Extended
count-key-data uses the Define Extend and Locate
Record commands to describe the nature and scope of
a data transfer operation to the storage control to
optimize the data transfer operation. See also
count-key-data
and
nonsynchronous operation.
extent
. A set of consecutively addressed tracks that a
channel program can access. The limits of an extent
are defined by specifying the addresses of the first and
last tracks in the extent.
G
gigabyte (GB)
. 10
9
I
ICKDSF
. See
Device Support Facilities program
input/output configuration program (IOCP)
. A
program that defines to a system all the available I/O
devices and the channel paths.
input/output (I/O) subsystem data rate
. The rate at
which data can be moved between processor storage
and a device during the data transfer portion of an I/O
operation. This rate is the lowest of either the channel
data rate, the control unit data rate, or the device data
rate.
M
media
. The disk surface on which data is stored.
media SIM
. A message generated when a storage
subsystem detects a problem with device media. You
must perform media maintenance using ICKDSF to
resolve the problem. See also
service information
message (SIM).
megabyte (MB)
. 10
6
bytes.
N
nondisruptive installation
. A capability that allows
users to access data in an existing storage subsystem
while installing additional devices in the subsystem.
nondisruptive removal
. A capability that allows users
to access data in an existing storage subsystem while
removing another device from the subsystem.
nonsynchronous operation
. A type of operation in
which the channel and storage control activities required
to end one command and initiate the next do not
necessarily occur within the inter-record gap between
two adjacent fields. Contrast with
synchronous
operation
Note:
With nonsynchronous operations, the channel
can be slower than the device while reading
information, and faster than the device while writing
information. Therefore, the time difference in processing
a channel program depends on the current operating
environment rather than on a property of the device or
storage control.
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