Viper 60s Theory Of Operation And Maintenance Manual page 57

VIPER SCSI 60,
125 &
150 THEORY OF OPERATION AND MAINTENANCE
4.25 Error Reporting
4.25.1 Soft Errors
A soft error is not considered an error, but more a reliability data indicator. Most soft
errors are tape-quality related, and will occur more frequently during write operations
than during read operations. Soft errors indicate repeated attempts (less than 16) by the
drive to read or write data on the tape. Some soft errors are normal, but an increase in the
usual count can indicate deteriorating tape quality. Retensioning the tape can lower the
soft error count. If the soft error count remains higher than normal, clean the read/write
heads. If this procedure does not clear the problem, change to a new tape cartridge.
4.25.2 Hard Errors
If a hard error (unrecoverable error) occurs during operation, the drive terminates opera-
tion immediately and returns a Check Condition. The Initiator ceases any further read or
write functions and issues a Request Sense Command to determine the type of error.
When the drive detects a write error, it attempts to rewrite this block of data up to fifteen
times on sequential blocks of tape. After the sixteenth attempt, the error is considered
unrecoverable and the operation terminates. When a hard error is encountered, retention
the tape then repeat the function. If successful ignore the hard error. If not successful,
replace the tape with a new tape cartridge and repeat the function.
4.26 SCSI Bus Phase Timing
Table 4-14 shows the SCSI Bus sequence timing. Except where noted, the delay time
measurements for each SCSI device is calculated from signal conditions existing at the
SCSI bus connection for that device. Normally these measurements do not consider delays
in the SCSI bus cable.
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