SCSI-3 PR, which stands for Persistent Reservation, supports multiple
nodes accessing a device while at the same time blocking access to other
nodes. SCSI-3 PR reservations are persistent across SCSI bus resets or node
reboots and also support multiple paths from host to disk. For SCSI-2 disks,
reservations are not persistent which means they do not survive node reboots.

    SCSI-3 PR uses a concept of registration and reservation. Systems that
participate, register a key with SCSI-3 device. Each system registers its own
key. Then registered systems can establish a reservation. With this method,
blocking write access is as simple as removing registration from a device. A
system wishing to eject another system issues a pre-empt and abort command
and that ejects another node. Once a node is ejected, it has no key
registered so that it cannot eject others. This method effectively avoids the
split-brain condition.  

 
To enable the SCSI3_Persistent_Reserve bit on Symmetrix/DMX for Oracle RAC
(or any instance where mutliple hosts need to have simultanious access to
volumes)

In configure.txt on your Solutions Enabler host.

    set device 0090 attribute=SCSI3_persist_reserv;

then from the command line:

    # symconfigure -sid 1234 -f configure.txt preview

    # symconfigure -sid 1234 -f configure.txt commit

Simple.    To verify that it was set, run the following:

# symdev -sid 1234 show 0090

And among the output youll find the following:

    SCSI-3 Persistent Reserve: Enabled



more /tmp/dpspdbl
set device 1cd,attribute=SCSI3_persist_reserv;
set device 1c9,attribute=SCSI3_persist_reserv;

symconfigure -sid 373 -file /tmp/dpspdbl preview
symconfigure -sid 373 -file /tmp/dpspdbl commit



#
# turn it off
#
Alternatively to removed the SCSI3 Persistent Reservation.

set device xxx attribute=no SCSI3_persist_reserv;

Eg :
set device 0138 attribute=NO SCSI3_persist_reserv;