gmirror is a tool for creating / managing software raid 1 under FreeBSD >= 5.3.

FreeBSD 5.3 or more with geom compiled in. (or with module)

If a disk fails, you should replace the disk and tell gmirror to resync the array. First, you'll need to identify the faulty disk:

#> gmirror status
#> gmirror list

Then, you should stop the FreeBSD host, and replace the faulty disk. Once the disks is changed, restart the host.

Now, you should reintegrate the new disk to the array:

(note: you should replace ad0 and gm0 with correct values you've identified before)

#> gmirror remove gm0 ad0
#> gmirror insert gm0 ad0

Now, enjoy reconstruction !

You could get informed on sync status:

#> gmirror status