We just upgraded fro ESX3.5 to ESX 4 U1 a few weeks back. We are running on a IBM Blade Center S with HS21-7995 blades and using the SAS RAID Module for Storage.
On two occasion all the ESX hosts stopped responding/VMS were offline and on console of each Host was displayed - SD 0:0:0:0 still retrying after 360s.
After power cycling the Blades and BCS Chassis, everything came back online.
Each hosts has a 20GB volume on the SAS RAID for BOOT that is mapped to the blade.
This install was stable for over a year on 3.5 and started this behavior after the upgrade . After the first time this occured I subsequently reloaded all the hosts with a fresh install of ESX4 U1 after wiping the volume. We experenced this again yesterday morning.
I will likely open a support case with Vmware and I am already talking to IBM as well. Any thoughts or suggestions are appreciated.