HP LTO-4 Technical Reference Manual page 44

Fibre Channel
filemark
immediate mode
infinite flush
LUN
SAN
sequential access
42
Fibre Channel provides an inexpensive yet expandable 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.
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.
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
command. On the other hand, data is not flushed to tape in response to a filemark
command.
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.
Logical Unit Number. A unique number by which a device is identified on the SCSI
bus. A tape drive has a fixed LUN of 0. In an autoloader, the changer mechanism is
LUN1.
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 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.
WRITE FILEMARKS