HP Ultrium Tape Drive User Manual download pdf (Page 35)

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.

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.

synchronous data transfer, the initiator and target work in synchronization,

allowing transmission of a packet of data to start before acknowledgment of the

previous transmission.

wide (16-bit) data transfer, two bytes are transferred at the same time instead of

a single byte.

HP Ultrium drives support asynchronous, synchronous and narrow (8-bit) wide

transfers.

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HP Ultrium Tape Drive User Manual Page 35