rhel8: KVM running, Unplugging the FC cable on hypervisor causes I/O errors on multipass passthrough.

Solution Verified - Updated -

Issue

We use the passthrough of multipath device. The multipath device(mpathab) on the host is recognized as /dev/sda on the guest.

     <driver name='qemu' type='raw' cache='none' io='native'/>
     <source dev='/dev/mapper/mpathab' index='3'/>
     <backingStore/>
     <target dev='sda' bus='scsi'/>
     <alias name='scsi0-0-0-0'/>
     <address type='drive' controller='0' bus='0' target='0' unit='0'/>

We unplugged 3 out of 4 FC cables at the same time for the testing. Then I/O error occurred on /dev/sda on the guest and filesystem became read-only.

    kernel: sd 0:0:0:0: [sda] tag#15 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_S>
    kernel: sd 0:0:0:0: [sda] tag#15 Sense Key : Aborted Command [current]
    kernel: sd 0:0:0:0: [sda] tag#15 Add. Sense: I/O process terminated
    kernel: sd 0:0:0:0: [sda] tag#15 CDB: Synchronize Cache(10) 35 00 00 00 00 00 0000>

    kernel: EXT4-fs (sda4): Remounting filesystem read-only

From the host log, I/O error occurred on the devices of mpathab, while multipathd detected the pass failure.
So in reality the filesystem went readonly, but we would expect that the remaining path handles the I/O.

Environment

  • Red Hat Enterprise Linux (RHEL) 8
  • multipath
  • KVM guest, passthrough configuration

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