Below is my partitions
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[root@localhost ~]# cat /proc/mdstat
Personalities : [raid1] [raid6] [raid5] [raid4]
md0 : active raid1 sdb1[1] sda1[0]
513984 blocks [2/2] [UU]

md1 : active raid1 sda3[0] sdb3[1]
309492160 blocks [2/2] [UU]

unused devices: <none>
[root@localhost ~]#
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Using MDADM, i get the following
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[root@localhost ~]# mdadm /dev/md0 --add /dev/sda1
mdadm: Cannot open /dev/sda1: Device or resource busy
[root@localhost ~]#
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i've created the array's following the guide
http://www.ping.co.il/node/1

and I've attempted to perform the hotadd operation in rescue mode booting with DVD.
I do not have any raid option's in my bios.

What am I missing?

Your assistance will be much appreciated.

Thank you,
Nathan.
itplanett@gmail.com

I've never had much luck with hot swapping RAID drives, even with expensive enterprise RAID hardware. You are better off to replace the bad disk, rebuild the array, then restore from backup.

The thing is, these are brand new SATA2 hard drives and this is a brand new installation of fedora 9 with all updates and kernel updates. I've followed every step accurately as outlined in the documentation.

even the mdadm --stop /dev/md0 returns a message saying "device or resource busy". I've looked around and am unable to get any leads on this.

I have "exactly" the same problem, any advice would be greatly appreciated