Quantum DLTtape DLT 4000, Product Manual

Page: 112 / 300

SCSI Commands
5-12 Quantum DLT 4000 Tape Drive
The DLT 4000 tape drive recognizes multiple, successive SCSI bus resets and
SCSI bus resets of arbitrarily long duration. The tape drive recovers within the
time limits specified above following the last SCSI bus reset.
5.1.7 Data Cache and Tape Write Interaction
The Quantum DLT 4000 drive contains a data cache that buffers blocks
(records) until they are written to tape. This section describes when those blocks
are written, or “flushed” to tape. A Mode Select parameter allows the data cache
to be disabled (unbuffered mode). In this mode, every WRITE command causes
data to be written to the tape medium before the STATUS byte and the
COMMAND COMPLETE message are returned to the host.
NOTE
Unbuffered mode is NOT recommended due to the poor
performance that may result.
The contents of the write data cache are written to the tape medium under the
following circumstances:
•
When two or more WRITE FILEMARKS commands are issued without
intervening tape motion commands.
•
When a WRITE 0 FILEMARKS command is issued.
•
When data has been in the cache longer than the maximum time specified by
the value of the Mode Parameter “Write Delay Time.”
•
When a non-write type media access command is received (for example,
SPACE, READ, UNLOAD).