Subject: [nfsv4] draft-ietf-nfsv4-scsi-layout-00

From: "J. Bruce Fields" <[email-masked]>
Date: Mon, 20 Jul 2015 11:46:48 -0400

What needs to be done to clear SCSI persistent reservations after an MDS
crash?:

	- Nothing, they're cleaned up automatically somehow.
	- The MDS issues some sort of blanket "clear all reservations"
	  command on restart.
	- The MDS issues commands to individually clear all the old
	  reservations.

I'm just curious what (if anything) we need to do for crash recovery or
failover in the scsi layout case.  Apologies if this is already dealt
with elsewhere.

--b.

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From: Christoph Hellwig <[email-masked]>
Date: Tue, 21 Jul 2015 13:02:17 +0200

Hi Bruce,

The reservation survices even if the MDS goes down.  Once the MDS is up
it can either re-use the existing key, or for extra caution register a new
one using the "REGISTER AND IGNORE EXISTING KEY" command.

The easiest strategy for a clustered MDS setup would be to have a
"Exclusive  Access – All Registrants" setup where the new MDS could
just take over, in a sligtly more sophisticated setup the MDS taking
over in a Active/Passive setup would PREEMPT the existing reservation.

All of this is out of scope for this RFC and an implementation details of
the MDS that's transparent to the client.