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Just curious: PowerPath on AIX and Group Reservations
Hi,
Those of you following the Symmetrix forum will not be surprised by this question.
In emc212199 it's mentioned that PowerPath on AIX translates the SCSI command RESERVE to the command PERSISTENT RESERVE OUT (which is what 0x5f stands for). This mechanism works, even on devices whose SCSI3_persist_reserv flag ("the PER flag") is not enabled.
When this flag is not enabled, it's not possible to place reservations on a device using the PERSISTENT RESERVE OUT command. But PowerPath seems to manage just fine anyway . How does PowerPath do this? Does it use some sort of "secret handshake" with the symm? (A special "magic" reservation key perhaps?)
Regards,
Jurjen Oskam
Brion2
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January 19th, 2011 12:00
Hi Jurjen. What we can say is that there is special handshaking between PowerPath and Symmetrix Enginuity code which allows support for standard AIX configurations when the PER bit is disabled. For AIX VCS implementations the PER is required to be enabled. I hope this helps.
Thanks, Brion
Jurjen_Oskam
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January 19th, 2011 22:00
Hi,
Thank you, that explains the situation. It's not that I'm interested in the exact contents of the handshake, but it's good to know there is one. You see, on the one hand the documentation states that a device will not normally accept persistent reservation commands, but on the other hand there's information that PowerPath uses those same persistent reservation commands to manage reservations. Without knowing that there's special handshaking, this information is a bit contradictory.
Regards,
Jurjen Oskam