Hi Guys, Finally managed to make the server agree to accept the new disk partition into the raid array by booting off an install CD into 'linux rescue', skipping the search for installed instances of CentOS and doing the following: mdadm -A --run /dev/md0 /dev/hda1 -- that got the existing /dev/md0 up and running with its one disk mdadm /dev/md0 -a /dev/hdg1 -- the usual stuff that wouldn't work before. Solution found in a forum thread on the CentOS Web site from September, so thanks to 'WhatsHisName'. Original post below for the curious: > Hi Guys, > > I have just replaced a faulty Max...woah, wait...this one's a > Seagate... IDE hard disk but I cannot remake the software raid pair. > > The currently running disk is hda and I am trying to add back hdg - > both are master drives on separate controllers. > > I have run fdisk on hdg and created the same partition structure as > had and changed their types to 'fd' but when I try and rebuild the > array I get: > > mdadm /dev/md0 -a /dev/hdg1 > > mdadm: hot add failed for /dev/hdg1: Invalid argument > > If I look at /var/log/messages, I have: > > Oct 5 16:04:39 petdoctors kernel: md: could not bd_claim hdg1. > Oct 5 16:04:39 petdoctors kernel: md: error, md_import_device() > returned > -16 > >>From other postings, this seems to imply the hdg1 partition is mounted >>but I > can find no evidence of this (df or cat /proc/mounts or lsof). I have > done sone googling and found others having fun with this but no > specific solution. > > Anyone?