HP 330834-B21 - StorageWorks Ultrium 460 Tape Library Drive Module, Техническое справочное руководство

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Glossary 39
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 Ultrium 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.
data transfer phase On a SCSI bus, devices put in requests to be able to transfer information.
Once a device is granted its request, it and the target to which it wants to
send information can transfer the data using one of three protocols (assuming
both devices support them): asynchronous, synchronous, and wide.
In
asynchronous transfers, the target controls the flow of data. The initiator
can only send data when the target has acknowledged receipt of the previous
packet. All SCSI devices must support asynchronous transfer.
glossary