What happens to running VMs if the datastore they're on goes offline?

[Faize]

I take it something unpleasant happens, but it'd be nice to know what that is and just how unpleasant it is...

[rcporto]

VM will may be unresponsive/crashed and after restore connection to the datastore you will may need do a hard reset.

[vickey0rana]

if the VM is powered on and the datastore become unavailable or disconnects, the VM would freeze all I/O while and remain in a ‘powered on’ state in ESXi or vSphere (of-course in this state VM cannot operate or respond to network as well) and VM name appears in italic characters in vCenter inventory.

Now if you forcefully power OFF those VMs then once Datastores are back, those VMs will be shown as greyed out in vSphere Client. At that point reload the VM from CLI or try to power ON from GUI and answer the prompted question like I copied\moved VM.

Hope will be also helpful for you.

~Ravinder S Rana

[Alistar]

I've had this happen once, so I'll just add in to what Richardson & Vickey have told before:

Only the VM's part that is cached in the RAM persists - that means the VM can still ping if its networking stack is cached, in case of a Windows Server machine, you could even RDP to it because that part of kernel/modules was present in the RAM as well, but after that you could only see a black screen and only a cursor - you can do nothing more. Depending on the connectivity loss duration, the IOs the VM itself wants to generate might be filling the guest OS' RAM (especially when the guest OS is a SQL Server) that would want to be flushed to the disk as soon as the connectivity is restored - if the connections don¨t time out and your RAM is filled, it can either shut the application down or result in a BSOD. It's really quite a lot of unpredictable funky stuff that can happen.

[brunofernandez1]

once i had a similar problem: our SAN wents offline and all VMs were greyed out.

After trying to reconnect the Datastores there was no way to do it. I also tried it from the console but the esxi was really leaking.

My last option was to reboot all esx server and then i was able to restart the vms.