HP LTO Ultrium 6 tape drives UNIX, Linux and OpenVMS configuration guide

Glossary
AT&T mode Berkeley and AT&T functional modes differ in “read-only” close functionality. In AT&T mode, a
device close operation will cause the tape to be repositioned just after next filemark on the tape
(the start of the next file).
Berkeley mode Berkeley and AT&T functional modes differ in “read-only” close functionality. In Berkeley mode
the tape position will remain unchanged by a device close operation.
BOT Beginning Of Tape. The first point on the tape that can be accessed by the drive.
buffered mode A mode of data transfer in write operations that facilitates tape streaming. It is selected by setting
the Buffered Mode Field to 1 in the SCSI MODE SELECT Parameter List header.
compression A procedure in which data is transformed by the removal of redundant information in order to
reduce the number of bits required to represent the data. This is basically done by representing
strings of bytes with codewords.
In LTO drives, the data is compressed using the LTO-DC compression format which is based on
ALDC (licensed from Stac/IBM) with two enhancements. One limits the increase in size of data
that cannot be compressed that ALDC produces. The other is the use of embedded codewords.
Fibre Channel Fibre Channel provides an inexpensive yet expendable means of quickly transferring data between
workstations, mainframes, supercomputers, desktop computers, storage devices, displays and
other peripherals. Although it is called Fibre Channel, its architecture represents neither a channel
nor a real network topology. It allows for an active intelligent interconnection scheme, called a
fabric, to connect devices. All a Fibre Channel port has to do is to manage a simple point-to-point
connection between itself and the fabric.
Several common ULPs (Upper Level Protocols) including IP and SCSI can run on Fibre Channel,
merging high-speed I/O and network functionality in a single connectivity technology.
filemark A mark written by the host to the tape that can be searched for, often using the drive’s fast-search
capability. It does not necessarily separate files. It is up to the host to assign a meaning to the
mark.
immediate mode A mode of responding to SCSI commands where the drive or other peripheral does not wait until
the command has finished before returning status information back to the host. For writing filemarks,
Immediate mode can significantly improve the performance of systems that do not set the Immediate
bit when sending a SCSI WRITE FILEMARKS command. On the other hand, data is not flushed
to tape in response to a filemark command.
infinite flush By default, the buffer in the drive is flushed every 5 seconds. Infinite flush avoids frequent starting
and stopping of the mechanism when using a very slow application. It also avoids losing capacity
through the flushing of partly written groups. On the other hand, infinite flush means that data
can remain in the buffer for very long periods of time, and could be lost in the event of a power
failure.
LUN Logical Unit Number, by which different logical units within a particular device can be addressed
individually. Each logical unit contains a device server. The drive provides a SSC device server,
typically at LUN 0, and an ADC device server, typically at LUN 7. Both may be reassigned, for
example the ADI automation controller may reassign the ADC LUN by using the ADC Device
Server configuration mode sub-page. Finally, the drive also provides optional SMC LUN(s), which
may be assigned by an ADI automation controller at the time of enablement, typically at LUN 1.
SAN Storage Area Network. A dedicated, high-speed network that establishes a direct connection
between storage elements and servers. The hardware that connects workstations and servers to
storage devices in a SAN is referred to as a fabric. The SAN fabric enables
any-server-to-any-storage device connectivity through the use of Fibre Channel switching technology.
sequential access Sequential access devices store data sequentially in the order in which it is received. Tape devices
are the most common sequential access devices. Devices such as disk drives are direct access
devices, where data is stored in blocks, not necessarily sequentially. Direct access allows speedy
retrieval, but is significantly more costly.
28 Glossary