User's Manual

DLT2000 SCSI Interface
8-4 DLT2000/DLT2700 Cartridge Tape Subsystem
8.2.6 Data Cache and Tape Write Interaction
The DLT2000 contains a data cache that buffers blocks (records) until they are written.
This section defines specific times that blocks shall be written to tape. A Mode Select
parameter allows the data cache to be disabled (unbuffered mode). In this mode, every
WRITE command will cause the data to be written to the media before the STATUS
byte and the COMMAND COMPLETE message is returned to the host. Unbuffered
mode is not recommended due to the poor performance that will result.
__________________________NOTE ____________________________
Unbuffered mode is not recommended due to the poor performance that
will result.
____________________________________________________________
The write data cache shall be written (flushed) to the media under the following
circumstances:
• When WRITE FILEMARKS command is issued with the immediate bit is set to
zero.
• When a WRITE 0 FILEMARKS command is issued.
• Data in the cache longer than specified by the value of the Mode Parameter "Write
Delay Time" shall be automatically written to media.
• When a nonwrite type media access command is received (for example, SPACE,
READ, UNLOAD, . . .)
•= When a SCSI Bus Reset or a Bus Device Reset message is received.
8.2.7 Other SCSI Functionality
1. Linked commands are supported.
2. Untagged queuing is supported.
3. The DLT2000 does not use the Wide-SCSI data path.
8.2.8 Bus Phases
The DLT2000 conforms to the bus state transition table shown in the SCSI-2 standard,
"Phase Sequences." The information in the following sections also applies.