User's Guide

Page 126 DDS-4 SCSI Interface Manual, Rev. B
RELEASE UNIT (17h / 57h)
The RELEASE UNIT command releases a current drive reservation, if the command
is received form the Initiator that originally established the reservation. If the original
reservation was made for a third party, the RELEASE UNIT command Descriptor
Block must also carry the third party data. Any RELEASE UNIT command that
arrives from other than the originating requester (including one that arrives from the
third party currently in command of the drive) is ignored and Good Status is returned
in response to the command.
þ Note: The 6-byte version of the RELEASE UNIT command uses opcode
17h; the 10-byte version uses opcode 57h. We recommend using the 10-
byte Release Unit Command since the older 6 byte command can only
specify a Device ID in the range of 0 to 7, whereas the drive supports a
Device ID in the range of 0 to 15.
Additional events and conditions that can cause a reservation to be released are
discussed under the RESERVE UNIT command.
þ Note: It is not an error to attempt to release an ID that is not currently
reserved to the requesting Initiator. A reservation cannot be released, if
another Initiator reserves it.
RELEASE UNIT Command Descriptor Block
6-byte version:
The following table shows the layout of the 6-byte CDB.
Byte
Bits
7 6 5 4 3 2 1 0
0 0 0 0 1 0 1 1 1
1 0 0 0 3rd Pty 3rd Pty ID 0
2 0 0 0 0 0 0 0 0
3 0 0 0 0 0 0 0 0
4 0 0 0 0 0 0 0 0
5 vendor unique* 0 0 0 0 Flag Link
* This vendor-unique field is reserved and must be set to zero.
The drive also supports the SCSI-3 10-byte Release Unit Command. The table
below shows the Descriptor Block for the 10-byte CDB.
þ Note: We recommend using the 10-byte Release Unit Command since the
older 6 byte command can only specify a Device ID in the range of 0 to 7,
whereas the drive supports a Device ID in the range of 0 to 15.