SCSI Commands
Quantum DLT 8000 Tape System
5-3
5.1.1 SCSI Pointers
SCSI architecture provides a set of three pointers (called saved pointers) for each I/O
process. The three pointers are Command, Status, and Data. When an I/O process
becomes active, the three saved pointers are copied to the initiator as current pointers.
There is only one set of current pointers in the initiator at one time. The current pointers
point to the next command, data, or status byte to be transferred between the initiator's
memory and the drive. The saved and current pointers reside in the initiator.
The saved command pointer always points to the start of the Command Descriptor Block
for the I/O process. The saved status pointer always points to the start of the status area
of the I/O process. The saved data pointer always points to the start of the data area until
the drive sends a SAVE DATA POINTER message for the I/O process back to the
initiator.
In response to the SAVE DATA POINTER message, the initiator stores the value of the
current data pointer into the saved data pointer for that I/O process. The drive can
restore the current pointer from the saved pointer value for the active I/O process by
sending a RESTORE POINTERS message to the initiator. The initiator then copies the
set of saved pointers into the set of current pointers. Whenever a drive disconnects from
the SCSI Bus, only the set of saved pointers is retained in the initiator. The set of
current pointers is restored from the set of saved pointers when the I/O process is
reconnected.
Summary of Contents for DLTtape DLT 8000
Page 1: ...DLTTM 8000 Tape System Product Manual Nov 10 2003 81 60118 06...
Page 5: ...USER MANUAL STATEMENTS FOR CLASS B EQUIPMENT continued...
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Page 26: ...Table of Contents xxiv Quantum DLT 8000 Tape System...
Page 36: ...About This Manual Quantum DLT 8000 Tape System xxxii...
Page 54: ...General Description and Specifications 1 18 Quantum DLT 8000 Tape System...
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Page 376: ...Appendix A Definition of Vendor Unique Sense Data Information A 4 Quantum DLT 8000 Tape System...
Page 386: ...Appendix C Updating the Firmware C 6 Quantum DLT 8000 Tape System...
Page 396: ...Appendix E Visual Inspection Procedure for DLTtape Cartridges E 8 Quantum DLT 8000 Tape System...
Page 406: ...Appendix G DLT 7000 Emulation Feature G 8 Quantum DLT 8000 Tape System...
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