SCSI Primary Commands - 2.pdf

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T10/1236-D Revision 20 18 July 20017.21 RESERVE(10) command7.21.1 RESERVE(10) command introductionThe RESERVE(10) command (see table 109) is used to reserve a logical unit.Table 109 — RESERVE(10) commandBitByte7 6 5 4 3 2 1 00 OPERATION CODE (56h)1 Reserved 3RDPTY Reserved LONGID Obsolete2 Obsolete3 THIRD-PARTY DEVICE ID4 Reserved5 Reserved6 Reserved7 (MSB)PARAMETER LIST LENGTH8 (LSB)9 CONTROLThe RESERVE and RELEASE commands provide the basic mechanism for contention resolution inmultiple-initiator systems. The third-party reservation allows logical units to be reserved for another specified SCSIdevice. See 5.5.1 for a general description of reservations and the commands that manage them.If the RESERVE(10) command is implemented, then the RELEASE(10) also shall be implemented.Byte 1 Bit 0 and Byte 2 provide an obsolete way to reserve extents within a logical unit. If Byte 1, Bit 0 is equal toone, device servers not implementing the obsolete capability shall terminate the command with CHECKCONDITION status and the sense key shall be set to ILLEGAL REQUEST.7.21.2 Logical unit reservationLogical unit reservations are mandatory if the RESERVE(10) command is implemented. This command shallrequest that the entire logical unit be reserved for the exclusive use of the initiator until the reservation is supersededby another valid RESERVE command from the same initiator or until released by a RELEASE commandfrom the same initiator that made the reservation, by a TARGET RESET task management function performed byany initiator, by a hard reset condition, or by a power on cycle. A logical unit reservation shall not be granted if thelogical unit is reserved by another initiator. It shall be permissible for an initiator to reserve a logical unit that iscurrently reserved by that initiator. If the LONGID bit or the 3RDPTY bit is zero then the PARAMETER LIST LENGTH fieldshall be ignored.If the logical unit is reserved for another initiator, the device server shall return RESERVATION CONFLICT status.After honoring a logical unit reservation, the device server shall check each newly received command for reservationconflicts. See 5.5.1.156 dpANS SCSI Primary Commands - 2 (SPC-2)
18 July 2001 T10/1236-D Revision 20For multiple port implementations, devices on other ports (i.e., the ports that do not include the initiator to which thereservation has been granted) also shall be denied access to the logical unit as described in the precedingparagraph.7.21.3 Third-party reservationThird-party reservations are mandatory if the RESERVE(10) command is implemented. The third-party reservationfor the RESERVE(10) command allows an application client to reserve a logical unit within a logical unit foranother SCSI device. This is intended for use in multiple initiator systems that use the COPY or EXTENDEDCOPY command.If the third-party (3RDPTY) bit is zero, then a third-party reservation is not requested. If the 3RDPTY bit is zero thenthe LONGID bit shall be ignored. If the 3RDPTY bit is one then the device server shall reserve the specified logicalunit for the SCSI device specified in the THIRD-PARTY DEVICE ID field. Device ID formats are protocol specific. Thedevice server shall preserve the reservation until it is superseded by another valid RESERVE command from theinitiator that made the reservation or until it is released by the same initiator, by a TARGET RESET taskmanagement function performed by any initiator, a hard reset condition, or by a power on cycle. The device servershall ignore any attempt to release the reservation made by any other initiator.After a third-party reservation has been granted, the initiator that sent the RESERVE command shall be treated likeany other initiator. Reservation conflicts shall occur in all cases where another initiator is not allowed access due tothe reservation.If independent sets of mode parameters are implemented, a third-party reservation shall cause the device server totransfer the set of mode parameters in effect for the application client that sent the RESERVE command to themode parameters used for commands from the third-party device. Any subsequent command issued by thethird-party device shall be executed according to the mode parameters in effect for the application client that sentthe RESERVE command.NOTE 34 This transfer of the mode parameters is applicable to device servers that store mode informationindependently for different initiators. This mechanism allows an application client to set the mode parameters of atarget for the use of a copy master (i.e., the third-party device). The third-party copy master may subsequentlyissue a MODE SELECT command to modify the mode parameters.If the THIRD-PARTY DEVICE ID value associated with the reservation release is smaller than 255, the LONGID bit maybe zero and the ID value sent in the CDB. Device ID formats are protocol specific. If the THIRD-PARTY DEVICE ID isgreater than 255, the LONGID bit shall be one. If the LONGID bit is one, the THIRD-PARTY DEVICE ID field in the CDBshall be ignored. If the LONGID bit is one, the parameter list length shall be at least eight. If the LONGID bit is oneand the parameter list length is less than eight, the device server shall return a CHECK CONDITION status with asense key of ILLEGAL REQUEST.Device servers that support device IDs greater than 255 shall accept commands with LONGID equal to one. Deviceservers whose devices IDs are limited to 255 or smaller may reject commands with LONGID equal to one withCHECK CONDITION status and a sense key of ILLEGAL REQUEST.dpANS SCSI Primary Commands - 2 (SPC-2) 157
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