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Quantum DLT 7000 Tape System 5-11
5.1.6 Behavior at Power-On and SCSI Bus Reset
The following apply to the DLT 7000 system tape drive’s behavior at power-on
and/or SCSI bus reset:
• When the Quantum DLT 7000 system is powered up, all device SCSI lines
are set to high impedance.
• The design of the DLT 7000 system tape drive does not allow it to generate
any spurious signals on the SCSI bus at power-on.
• Within five seconds of power-on, and within 250 milliseconds (typically
under 4 milliseconds) after a SCSI bus reset, the DLT 7000 system tape
drive responds to SCSI bus selections and returns appropriate, normal
responses. Tape motion commands will be returned with Check Condition
status, Sense Key Not Ready, until the tape medium has been made ready.
• The tape drive implements the hard bus reset option.
• The tape medium is rewound to Beginning of Tape (BOT).
The DLT 7000 system tape drive recognizes multiple, successive SCSI bus resets
and SCSI bus resets of arbitrarily long duration. The tape drive recovers within
the time limits specified above following the last SCSI bus reset.
The tape drive goes through a calibration process at power up and loading of
medium.
5.1.7 Data Cache and Tape Write Interaction
The Quantum DLT 7000 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.
NOTE
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.