The replacement drive for my 1TB RAID5 finally came in last night. I had never actually had to do a rebuild with the md toolset before (I’ve always had hardware support in the past). I wasn’t able to find any rebuild option in OpenFiler’s web interface, so I ssh’ed in.
First, I looked at the partition structure of one of the remaining working drives with fdisk -l /dev/sdd, then I matched this partition setup on the replacement drive. Then I added the new drive back into the array with mdadm /dev/md1 -a /dev/sde1, and monitored the rebuild process occasionally by looking at /proc/mdstat.
The total time for the array rebuild was just shy of 4 hours and 30 minutes, on an Atom N270.