[ClusterLabs] fence-scsi question

Dan Swartzendruber dswartz at druber.com
Sun Feb 9 19:07:01 EST 2020

I have a 2-node CentOS7 cluster running ZFS.  The two nodes (vsphere 
appliances on different hosts) access 2 SAS SSD in a Supermicro JBOD 
with 2 mini-SAS connectors.  It all works fine - failover and all.  My 
quandary was how to implement fencing.  I was able to get both of the 
vmware SOAP and REST fencing agents to work - it just isn't reliable 
enough.  If the vcenter server appliance is busy, fencing requests 
timeout.  I know I can increase the timeouts, but in at least one test 
run, even a minute wasn't enough, and my concern is that too long 
switching over, and vmware will put the datastore in APD, hosing guests. 
  I confirmed that both SSD work properly with the fence-scsi agent.  
Fencing the host who actively owns the ZFS pool also works perfectly 
(ZFS flushes data to the datastore every 5 seconds or so, so withdrawing 
the SCSI-3 persistent reservations causes a fatal write error to the 
pool, and setting the pool in failmode=panic will cause the fenced 
cluster node to reboot automatically.)  The problem (maybe it isn't 
really one?) is that fencing the node that does *not* own the pool has 
no effect, since it holds no reservations on the devices in the pool.)  
I'd love to be sure this isn't an issue at all.

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