Also historically Sun StorEdge disk arrays would report success on a sync once the data was transferred to the appliance, because they had a write-back battery

Also historically Sun StorEdge disk arrays would report success on a sync once the data was transferred to the appliance, because they had a write-back battery that would allow the array time to finish writing the data even on sudden power interruption. Unfortunately for me, they also had a thing where if a write-back battery passed a certain number of hours in operation the array would no longer trust it and defaulted to then not using it at all - which is entirely reasonable right up until the point where your systems team won't buy a replacement. I once offended the lead sysadmin at that job on a phone call so much that he had to pass me off to his junior because I'd been telling him for months that the battery needed replacing and basically my opinion was "yeah, have fun waiting an hour while that system fscks" interspersed with helpless laughter. (in my defence, I wasn't paid to be on call and he called me at 2am during a good friend's 30th birthday party, so my capacity for diplomacy was even more limited than normal)