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logical block address (LBA)
The address assigned by the DS8000 to a
sector of a disk.
logical control unit (LCU)
See control-unit image.
logical data unit
A unit of storage that is accessible on a
given device.
logical device
The facilities of a storage server (such as
the DS8000) associated with the
processing of I/O operations directed to a
single host-accessible emulated I/O
device. The associated storage is referred
to as a logical volume. The logical device
is mapped to one or more
host-addressable units, such as a device
on a zSeries I/O interface or a logical unit
on a SCSI I/O interface, such that the host
initiating I/O operations to the
I/O-addressable unit interacts with the
storage on the associated logical device.
logical partition (LPAR)
For zSeries, a set of functions that create
the programming environment in which
more than one logical partition (LPAR) is
established on a processor. An LPAR is
conceptually similar to a virtual machine
environment except that the LPAR is a
function of the processor. Also, the LPAR
does not depend on an operating system
to create the virtual machine environment.
logical path
1) The relationship between a channel
image and a control-unit image that
designates the physical path to be used
for device-level communications between
these images. The logical path is
established as part of the channel and
control-unit initialization procedures by the
exchange of link-level frames.
2) With the Remote Mirror and Copy
feature, the relationship between a source
logical subsystem (LSS) and a target LSS
that is created over a physical path
through the interconnection fabric that is
used for Remote Mirror and Copy
functions. An LSS is a primary control unit,
which performs the functions of a channel
image.
logical subsystem (LSS)
A topological construct that consists of a
group of up to 256 logical devices. A
DS8000 can have up to 16 CKD-formatted
logical subsystems (4096 CKD logical
devices) and also up to 16 fixed-block
logical subsystems (4096 fixed-block
logical devices). The logical subsystem
facilitates configuration of the DS8000 and
might have other implications relative to
the operation of certain functions. There is
a one-to-one mapping between a CKD
logical subsystem and a zSeries
control-unit image.
For zSeries hosts, a logical subsystem
represents a logical control unit (LCU).
Each control-unit image is associated with
only one logical subsystem. See also
control-unit image.
logical unit
In open systems, a logical disk drive.
logical unit number (LUN)
In the SCSI protocol, a unique number
that is used on a SCSI bus to enable it to
differentiate between separate devices,
each of which is a logical unit.
logical volume
The storage medium that is associated
with a logical disk drive. A logical volume
typically resides on one or more storage
devices. The DS8000 administrator
defines this unit of storage. The logical
volume, when residing on a
RAID-formatted array, is spread over the
drives in the array.
logical volume manager (LVM)
A set of system commands, library
routines, and other tools that allow the
user to establish and control logical
volume storage. The LVM maps data
between the logical view of storage space
and the physical disk drive module.
longitudinal redundancy check (LRC)
1) A method of error checking during data
transfer that involves checking parity on a
row of binary digits that are members of a
set that forms a matrix. Longitudinal
redundancy check is also called a
longitudinal parity check.
2) A mechanism that the DS8000 uses for
locating errors. The LRC checks the data
as it progresses from the host, through
theDS8000 controller, into the device
adapter, and to the array.
340 IBM TotalStorage DS8000: Messages Reference