Bloody UPS problems again (?). Nodes n0003 & n0004 died and then successfully restarted o/n. No sign in the logs of a power failure of sufficient length to be recorded. The other two nodes connected to the same UPSs stayed up-and-running. The load on all UPSs is the same (at ~80%). Current working hypothesis is that even very short power disturbances are sufficient for killing the two GPU-loaded nodes. But why shouldn't this also be the case for n0001 & n0002 ?

Ignore the above (???). For nodes n0003, n0004 & n0006 chassis fans not functional. Could this be it ? Will have to wait …

Again power failures, again nodes not responding to wake-on-LAN. Re-wired UPSs as follows :

Following the re-wiring, the UPSs (at full load) stabilized at ~80%. We'll see how this goes. Took the opportunity to clear the head nodes' CMOS and re-gain the two 'lost' cores. To wrap this whole UPS story up, I should have bought 700 VA APC units two years ago and not this 'green-friendly' nonsense …