Two weeks ago we blew a breaker and the UPS that was supposed to keep the ReadyNAS up went down. The ReadyNAS didn't want to reboot after that.
The ReadyNAS Forum pointed me in the right direction, and I was able to boot the unit to the point that it identified a bad drive. It wouldn't identify which drive, which pretty much means that it was drive #1. It also suggested that I boot the unit without the (probable) offending drive.
That got the machine up in compromised mode; the data was still all there, but the performance was subpar and there was no redundancy; if another drive failed it was curtains.
I ticketed the problem out to Netgear and got routed to their super-secret ReadyNAS direct support line. They were all ready to RMA me out a replacement drive, but it turns out that the reseller I bought from stocked the unit with different drives (Hitachi) than Netgear uses (Seagate).
I decided to order a replacement Hitachi drive, get it in, and then return the bad Hitachi drive for warranty replacement. The new drive just came in yesterday.
So how hard is it to replace the disk? Remove the bad drive from the carrier (4 screws), put the new drive in the carrier, hot-plug it back in. The rest is magic, and about 6 hours later the unit reported that the RAID sync was complete and redundancy was restored.
I'm very happy with the ReadyNAS service group, and the product itself performed beautifully. We'll see how Hitachi stands up to this standard.