Scsi Sync (Address 02); Space Write (Address 03); Write Eot (Address 04) - Qualstar 1260 User Manual

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7.12.3 SCSI Sync (Address 02)
o
= DISALLOW, 1 = ALLOW; DEFAULT = 1
The SCSI PCBA supports both synchronous and asynchronous data transmission. De-
ciding which mode to use is a matter of initiator/target negotiation.
ALLOW - If the initiator selects the synchronous mode, the drive will transfer data in
the synchronous mode;
DISALLOW - If the initiator selects the synchronous mode, the drive will inform the
initiator that it will not operate in the synchronous mode, and will instead operate
only in the asynchronous mode.
7.12.4 Space Write (Address 03)
o
= NORMAL, 1 = READ AHEAD; DEFAULT = 0
Issuing a Read or Read Reverse command places the drive in the Read mode. When in
the Read mode, the drive mayor may not perform a read-ahead operation, depending
upon the setting of the Read Ahead option (see Section 7.12.16 for details on this op-
tion). Issuing a Write command to the drive places it in the Write mode, where there
is no read-ahead operation.
This parameter determines what the drive will do if it receives a Space Blocks com-
mand when it is in the Write mode:
• NORMAL - After spacing across the specified number of blocks, the drive
stops the tape immediately. It does not switch into the Read mode or perform a
read-ahead operation.
• READ AHEAD - After spacing across the specified number of blocks, the drive
switches to the Read mode and continues to move tape and to read blocks into
the buffer until the buffer is full (i.e., it performs a read-ahead operation.) This
is advantageous if the next command is a Read or Read Reverse command, be-
cause the data will already be in the buffer and will be immediately available
to the host. However, if the next command is a Write command, a delay will oc-
cur while the drive moves the tape back across all the blocks which were read
ahead into the buffer. Only after this delay will the drive request data from the
host.
7.12.5 Write EDT (Address 04)
0= WRITE, 1 = RETAIN; DEFAULT = 0
This parameter determines whether or not the drive will write the contents of the buf-
fer to tape when buffer operations are enabled and the EOT marker is sensed while
writing.
• WRITE -
All unrecorded data in the buffer will be written to tape and the
drive will then report an End Of Medium Check Condition with the Informa-
tion Bytes set to zero;
Supplemental SCSI Drive Information
7-19