I was getting DMA timeout errors on a FreeNAS server setup yesterday, so I "forgot" the drive, then removed it from the array, and today I've just swapped out the physical drive.
Strange, but I can't format the new drive, so now I'm "inserting" it into the existing one drive RAID 1 array. Hmmm, something about unable to store metadata. I might have to start over. Isn't that why its good to have RAID 1 in the first place, so you don't have to start over?
It appears that my SATA drives do not play well with power management, at all. Whenever I would try to format a drive, it would get kicked out and disappear entirely.
Also turns out that I had to completely format the old RAID1 member before creating a new one, it kept on finding the old RAID and trying to set that one up. I think I've run into that problem before...