500300 Rev. U
SCSI Configuration
5-3
where there is no read-ahead operation. If the drive receives a Space Blocks
command when it is in the Write mode, two courses of action are possible:
•
READ AHEAD
- After spacing across the specified number of blocks, the drive
switches to the Read mode and continues to move tape and read blocks into the
buffer until the buffer is full (i.e., perform a read-ahead operation.) This is
advantageous if the next command is a Read or Read Reverse command,
because the data will already be in the buffer and will be instantly available to
the host. However, if the next command is a Write command, a delay will occur
while the drive moves the tape forward across all the blocks that were read
ahead into the buffer. Only after this delay will the drive request data from the
host;
•
NORMAL
- The drive does not switch into the Read mode or perform a read-ahead
operation after spacing across the specified number of blocks; it stops the tape
immediately.
5.1.6
Unload (Default = Normal)
The Unload parameter determines how the tape drive responds to an Unload
command:
•
NORMAL
- The tape drive will rewind and unload the tape.
•
INHIBIT
- No tape motion will occur.
•
REWIND
- The tape drive will rewind the tape but will not unload it.
5.1.7
Write CER (Default = Error)
This parameter determines what the drive will report after the final write retry of a
block. Note that if the drive is eventually able to write the data correctly, the first
three choices prevent the drive from reporting that retries took place, while the last
two choices force the drive to report that recovery action occurred. In any event, the
drive will always report a Media Error if an operation ends in a hard error.
The following three choices prevent the drive from reporting the occurrence of
retries:
•
ERROR
- Use this choice to force the drive to report correctable write errors as
Media Errors rather than Recoverable Errors. If retries were required but the
final write retry was successful, the drive reports a Good Completion status.
•
LAST
- Use this choice if you want the drive to report the status of the last retry
operation rather than the status of the block. If the block was successfully
written, the drive reports a Good Completion status. If it resulted in a CER, the
drive reports a Recoverable Error. Otherwise, the drive reports a Media Error.
•
NO
- Use this choice to force the drive to report a Good Completion status if a
CER occurs.
The following two choices force the drive to report the occurrence of retries:
