BackBlaze have been frequently posting notes on their experience with running large numbers of hard drives in their storage service. Some salient points: * “Enterprise” drives, while more expensive than “consumer” ones, are not significantly more reliable. (This has been borne out by other studies.) * Keep your drives running all the time, or switch them off when not in use? “Our vote is to keep them running.” * They do use SMART to keep an eye on their drives. Other studies I read reported that these only picked up a minority (around 30%) of failures, from which I concluded that SMART was not worth using. I suppose it’s different for these guys if it saves on costs to replace a drive *before* it actually starts reporting uncorrectable errors... <https://www.backblaze.com/blog/hard-drive-stats-faq/>