User's Manual

DLT2000 SCSI Interface
DLT2000/DLT2700 Cartridge Tape Subsystem 8-3
8.2.4 Unit Attention Condition
Queued Unit Attentions are implemented on this device, and are maintained separately
for each valid LUN for each Initiator. Unit Attentions will be created in the following
circumstances:
• Power on
• BUS Reset
• Bus Device Reset message
• When the media may have changed asynchronously
• Another initiator changed the Mode Parameters
• A firmware (microcode) update has completed
Two queued Unit Attentions are not unusual. For example, if a unit is powered up and a
cartridge is loaded, Power Up and Not-ready to Ready Transition Unit Attentions are
created. Due to a limited number of Unit Attention buffers, if an initiator does not clear
Unit Attentions queued for it, at some point the tape device will stop generating new
Unit Attentions for that I-L combination (but existing ones will be left queued).
A LOAD command will not generate a Unit Attention for the initiator that issued the
command, since the transition to ready is synchronous.
8.2.5 Behavior Around Power-On and SCSI Bus Reset
• All device SCSI lines shall go to high impedance when the DLT2000 is powered
off.
• The DLT2000 will not generate any spurious signals on the SCSI bus at power-on.
• Within 5 seconds of power on, and within 250 milliseconds (typically under 4 ms)
after a Bus Reset, the DLT2000 will respond to SCSI bus selections and return
appropriate, normal, responses. Tape motion commands will be returned with
Check Condition status, Sense Key Not Ready, until the media has been made
ready.
• The Hard Bus Reset option is implemented.
•= Cached write data are flushed to the media upon bus reset.
• The media is rewound to BOP (Beginning of Partition, i.e. Beginning of Tape).
The DLT2000 will be able to recognize multiple bus resets in succession and bus resets
of arbitrarily long duration. It will recover within the time limits specified above,
following the last bus reset.