Hi EBoucq,
This sounds like a storage issue or a network getting maxed out.
What kind of storage are you using FC or iSCSI/NFS?
Also at the time of the event, what does the logs say?
check /var/log/messages (if this is ESXi)
or /var/log/vmkernel (if this is ESX)
Also check the physical switch stats. Do you see any packet drops or anything else that looks out of place for the port and switch on which the host is connected?
Regards
a