We have a 16-drive RAID-6 that has three problem drives. Two are already dead, and the third is giving SMART warnings. (Nevermind how it got in such a bad state.)
Obviously we want to replace the dead drives before the one that is still working, but is it better to:
replace one dead drive, let the RAID rebuild, then replace the other, and let it rebuild again; or
replace both drives at once and let it rebuild both in parallel?
To put it another way, will we get back to a state of redundancy faster by reintroducing one drive or two? Does rebuilding two drives in parallel slow the rebuild process?
In case it matters, the controller is a 3ware 9650SE-16ML.