Status Update - I added a new disk group to Pool A.
Pool A already holds the two esxi DataStores - I rebooted one of my ESXI hosts - Bang! the DataStores will no longer mount.
Looking in vmkernel.log I see the following message
2019-03-21T16:09:32.361Z cpu7:2097364)WARNING: Vol3: 3102: XXXXXX1/5c91215c-80529b43-df3a-5cb901cf9580: Invalid physDiskBlockSize 512
2019-03-21T16:09:22.301Z cpu2:2097364)FSS: 6092: No FS driver claimed device '5c91218e-9ca78e9c-4f5d-5cb901cf9580': No filesystem on the device
Is this problem caused by an incompatibility between the MSA Firmware GL225R003 and ESXi 6.7 ?