One single HV (a hypervisor; the physical machine that hosts your virtual server) crashed.
Thanks for our distributed storage technology platform, all virtual servers that were hosted in it were automatically migrated over to other HVs.
Each HV hosts several dozen virtual servers, and each data center is made up of hundreds or thousands of these HVs.
This HV will now be taken out of production for further testing.
Impact: 15 minutes.