Data Cache And Tape Write Interaction - Quantum DLT 8000 Product Manual

SCSI Commands
5.1.7

Data Cache and Tape Write Interaction

The Quantum DLT 8000 system tape 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.
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" (the default is 20 seconds).
When a non-write type media access command is received (for example, SPACE,
READ, UNLOAD, LOCATE, ERASE).
5-12
NOTE
Quantum DLT 8000 Tape System