The last time I had to do a rebuild on the RAID it took a full two days to build.

This in itself wasn't so bad (read: I expected this from the last time), but I had to do it because the NAS was finding errors (Current Pending Sector) on the disks that it couldn't fix, but which turned out to be imaginary (i.e. a long format in windows not only cleared the CPS errors but didn't reallocate the sectors, so they all were fine). But if one of those disks died, the whole thing would go, so I needed to fix it.

So of the five disks, three had these errors, requiring three long-formats in Windows of 1.5 TB disks (the NAS is old and even 1.5 is pushing it with size).

By the end of the process I'd lost four days. Then another three days copying files back. from various backups. Fun fun.

And since it's a RAID drive the preformatting doesn't help, so I just hope I don't need to do it again any time soon.

That or fix current pending sector faults. Thankfully it works, because these were not the first, but they were the first I refused to RMA.