If the "crash on the server` is a crash of the target side, then the iSCSI initiator will typically re-establish the session using the same session ID. The Linux and Windows initiators behave like this. A great part of the resiliency of iSCSI lies in its ability to recover session state independently from the transport protocol. In this case, it is not necessary to clear the reservation; the initiator retains it.
If the crash is on the initiator side, then you're right, unless the session is persistently recorded (on Linux, it's not), the session gets a new session ID. At this point, this is where the PERSISTENT RESERVE OUT - PREEMPT or PREEMPT AND ABORT commands come in. Clusters that use persistent reservations as a way of coordinating access to shared storage all have to deal with the case where you need to take over a reservation held by another initiator. This is what an SPC-4 draft says about the commands:
An application client may preempt the persistent reservation with
another persistent reservation by issuing a PERSISTENT RESERVE OUT
command with PREEMPT service action or PREEMPT AND ABORT service
action with the following parameters:
a) RESERVATION KEY field set to the value of the reservation key that
is registered with the logical unit for the I_T nexus;
b) SERVICE ACTION RESERVATION KEY field set to the value of the
reservation key of the persistent reservation to be preempted; and
c) TYPE field and SCOPE field set to define a new persistent
reservation. The SCOPE and TYPE of the persistent reservation created
by the preempting I_T nexus may be different than those of the
persistent reservation being preempted.
Here, your initiator would come up, and execute a PERSISTENT RESERVE OUT - REGISTER command to register its nexus. Then, it calls PERSISTENT RESERVE IN - READ RESERVATION and READ KEYS or perhaps just READ FULL STATUS to retrieve the key for the initiator that holds the reservation. Finally, it executes PREEMPT AND ABORT to move the old reservation over to its new nexus.
Source: (registration required) http://www.t10.org/cgi-bin/ac.pl?t=f&f=spc4r35a.pdf (If you search around the web for spc4.pdf, you'll no doubt find a registration-free variation.)
