Thanks. After playing with it I figured out I'd still have an md superblock for the mirrored array on my disk. I was hoping I could accomplish everything without taking it offline -- I guess not. P.S. - In case anyone is following along; I'm actually booting from a separate mirrored boot partition (/boot). The RAID5 array holds /, /var, and /home. I won't need to make any changes in GRUB since I'm leaving that array alone. The last I heard, you can't boot from RAID5. Sidney Cammeresi wrote: > On Thu, 11 Jan 2007 at 06.35.40 -0600, Dave Alitz wrote: > >> I'm starting with 4 drives. Two active in the current mirror and two >> unused. The process I'm considering: >> >> Fail and remove a drive from the current md mirror, leaving three >> unused drives >> Create a new RAID5 array >> Add the new md RAID5 device as a member of the degraded mirror >> > > RAID1 doesn't work the way you think it does. You'll end up with a > degraded RAID1 made from a RAID5. It will work though. > > I recommend creating a degraded RAID5 from your two unused disks and > doing a copy to the new array. After the data are copied, fail one disk > out of the old array and add it to the new array, which will cause parity > to be computed. After that's done, nuke the old array and add the last > disk to the new array as a hot spare. > > This way, you end up with one array composed of physical disks, and your > data are always in two places throughout the process. > >