There has been a discussion on whether should install ESXi image in USB device. Per my personal experience, I do not recommend it.
I heard that a certain type of HP blade servers have issues of installing ESXi in the USB device a while ago. And I personally experienced a couple times in IBM HX5 blade servers. Unfortunately, one of our servers ran into this issue again today.
When it happens, the symptom is that it takes a long time to respond (up to 5 minutes) when you click the host in the vSphere client. And sometimes, you can get the error message as below.
I found the error message ‘Lost connectivity to storage device mpx.vmhba32…’ in the Tasks&Events tab of that host. Obviously, for some unknown reasons, the USB has been detached from the server. As we use embedded USB drive, I don’t think someone unplugged it. It must be caused the faulty USB interface or the USB drive.
The /bootbank, /altbootbank, /storage are all the partitions on USB devices. After I ran ‘ls –alh /vmfs/volumes’, it took a loooooooong time to return the results. And eventually it returns the connection timeout error.
This issue should not impact any running virtual machines, as all the ESXi image has been loaded in the memory. But the host is unable to save the changes permanently if there are any (the configuration backup daemon is a cron job /sbin/auto-backup.sh). All modifications will be lost after reboot. The only solution we have is to open a support ticket to replace the faulty USB device.
Reference: What is the ‘Lopsided bootbank’?