Morning,
Let's see if I can answer this one:
Lets say the active SP for LUN number 43 craps out on an Active-Passive array. At some point the ESXi host should detect the failure (if nothing else, during its every-five-minutes SAN scan), and if its doing multipathing then the PSA will revisit the claim rules and make up a new path table or whatever its called. But does the array notify the host? I'm thinking that maybe if its a Fibre Channel SAN, the RSCNs flying around will hit the HBA and hopefully the HBA driver will pass the notification up to the PSA, but I haven't read anything to that effect.
->First of all it depends if it's a active/passive or AULA arrary. It also depends on the location of the failure. Let's look at the possible locations for failure (array,cable,switch/switches,hba) each will have a different behavior. Let me play out some examples:
1. Active / passive array ( AULA)
Failure location:array (this would be a storage controller failure) scsi sense command from esxi host fails or array notifies the host via scsi command that the active path has moved. PSA switches path based upon policy
Failure location:cable SCSI sense commands fail and host does a lun tresspass letting the array know it wants to access the lun on the other path. Array swiches ownership and IO continues
Failure location: Switch/Switches same as cable
Failure location:HBA depends on issue if driver maybe nothing happens other than IO breaks. If it's failed then OS knows and initiates tresspass.
I really need to write a blog article on this matter I should get one posted in the next day or two. If you have more questions keep asking I will help me figure out what to include.
Thanks,
J