SCSI Primary Commands - 2.pdf

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T10/1236-D Revision 20 18 July 2001Table 11 — PERSISTENT RESERVE OUT service actions that are allowed in the presence of variousreservationsCommand Service ActionAddressed LUis reserved byanother initiator[A]Addressed LU has this type ofpersistent reservation held byanother initiator[B]Command isfrom aregisteredinitiatorCommand isfrom a notregisteredinitiatorCLEAR Conflict Allowed ConflictPREEMPT Conflict Allowed ConflictPREEMPT & ABORT Conflict Allowed ConflictREGISTER Conflict Allowed AllowedREGISTER AND IGNORE EXISTING KEY Conflict Allowed AllowedRELEASE Conflict Allowed a ConflictRESERVE Conflict Conflict ConflictKey: LU=Logical Unita The reservation is not released (see 5.5.3.6.2).The time at which a reservation is established with respect to other tasks being managed by the device server isvendor specific. Successful completion of a reservation command indicates that the new reservation is established.A reservation may apply to some or all of the tasks in the task set before the completion of the reservationcommand. The reservation shall apply to all tasks received by the device server after successful completion of thereservation command. Any reserve/release command or persistent reserve service action shall be performed as asingle indivisible event.Multiple reserve/release commands or persistent reserve service actions may be present in the task set at thesame time. The order of execution of such commands is defined by the tagged queueing restrictions, if any, buteach is executed as a single indivisible command without any interleaving of actions that may be required by otherreservation commands.5.5.2 The Reserve/Release management methodThe reserve/release management method commands, RESERVE(6), RESERVE(10), RELEASE(6), andRELEASE(10) are used among multiple initiators that do not require operations to be protected across initiatorfailures (and subsequent hard resets). The reserve/release reservations management method also allows anapplication client to provide restricted device access to one additional initiator (a third-party initiator), usually atemporary initiator performing a service for the application client sending the reservation command.Reservations managed using the reserve/release method do not persist across some recovery actions (e.g., hardresets). When a target performs one of these recovery actions, the application client(s) have to rediscover theconfiguration and re-establish the required reservations. Reserve/release managed reservations are retained bythe device server until released or until reset by mechanisms specified in this standard.The RESERVE(6) and RESERVE(10) commands allow superseding reservations.26 dpANS SCSI Primary Commands - 2 (SPC-2)
18 July 2001 T10/1236-D Revision 205.5.3 The Persistent Reservations management method5.5.3.1 Overview of the Persistent Reservations management methodThe persistent reservations management method is the mechanism specified by this standard for use by multipleinitiators that require operations to be protected across initiator failures, which usually involve hard resets.Persistent reservations persist across recovery actions, to provide initiators with more detailed control over reservationsrecovery. Persistent reservations are not reset by the TARGET RESET task management function or otherglobal actions.Persistent reservations for failing initiators may be preempted by another initiator as part of the recovery process.Persistent reservations shall be retained by the device server until released, preempted, or cleared by mechanismsspecified in this standard. Even though different protocols that transport SCSI commands handle hard resetsdifferently (e.g., parallel uses a reset signal, fibre channel loops use primitive signals) the persistent reservationshall be preserved. Optionally, persistent reservations may be retained when power to the target is removed.The PERSISTENT RESERVE OUT and PERSISTENT RESERVE IN commands provide the basic mechanism fordynamic contention resolution in multiple initiator systems using multiple port targets. Before a persistent reservationmay be established, an initiator shall register with a device server using a reservation key. Reservation keysare necessary to allow:a) authentication of subsequent PERSISTENT RESERVE OUT commands;b) identification of other initiators that are registered;c) identification of the reservation key(s) that have an associated reservation;d) preemption of a persistent reservation from a failing or uncooperative initiator; ande) multiple initiators to participate in a reservation.The reservation key provides a method for the application client to associate a protocol-independent identifier withan initiator on a specific port of a device server. The reservation key is used in the PERSISTENT RESERVE INcommand to identify which initiators are registered and which initiator, if any, holds the reservation. The reservationkey is used in the PERSISTENT RESERVE OUT command; to register an initiator, to verify the initiator issuing thePERSISTENT RESERVATION OUT command is registered, and to specify which initiator’s registration orpersistent reservation to preempt.Reservation key values may be used by application clients to identify initiators, using application specific methodsthat are outside the scope of this standard. This standard provides the ability to register no more than one key perinitiator/logical unit pair. Multiple initiators may use the same key for a logical unit. An initiator may establish registrationsfor multiple logical units in a SCSI device using any combination of unique or duplicate keys. These rulesprovide the ability for an application client to preempt multiple initiators with a single PERSISTENT RESERVE OUTcommand, but they do not provide the ability for the application client to uniquely the initiators using thePERSISTENT RESERVE commands.5.5.3.2 Preserving persistent reservationsThe application client may request activation of the persist through power loss device server capability to preservethe persistent reservation and registrations across power cycles by setting the APTPL bit to one in PERSISTENTRESERVE OUT parameter data sent with a REGISTER, or a REGISTER AND IGNORE EXISTING KEY serviceaction.After the application client enables the persist through power loss capability the device server shall preserve allcurrent and future registrations and persistent reservations associated with the logical unit to which the REGISTERor the REGISTER AND IGNORE EXISTING KEY service action was addressed until an application client disablesthe persist through power loss capability. The APTPL value from the most recent successfully completeddpANS SCSI Primary Commands - 2 (SPC-2) 27
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