System configuration is an HP320 G2 with ATA RAID controller and 2
disks.

RedHat Enterprise Linux version 4 ships the dmraid:

cat /etc/redhat-release
Red Hat Enterprise Linux AS release 4 (Nahant Update 2)

rpm -q dmraid
dmraid-1.0.0.rc8-1_RHEL4_U2

If you have previously configured the disks using a RAID configuration
then updated to JBOD the remnants of the former configuration will
still be on the 2nd disk, /dev/hdc:

cat /proc/partitions
major minor #blocks name

3 0 78150744 hda
3 1 76107906 hda1
3 2 2040255 hda2
22 0 78150744 hdc
22 1 78148161 hdc1
253 1 78150743 dm-1
253 2 78148161 dm-2

Partitioning and filesystem creation on /dev/hdc and /dev/hdc1 will
work without errors but mounting the filesystem will result in "busy"
errors:

mount -t auto /dev/hdc1 /mnt
mount: /dev/hdc1 already mounted or /mnt busy

Solution to this problem was to deactivate dmraid and create new
filesystem on /dev/hdc1:

dmraid -a no
mkfs.ext3 /dev/hdc1

Partitions following deactivation and filesystem creation:

cat /proc/partitions
major minor #blocks name

3 0 78150744 hda
3 1 76107906 hda1
3 2 2040255 hda2
22 0 78150744 hdc
22 1 78148161 hdc1


Other files of interest in debugging dmraid are /etc/blkid.tab and
directory /dev/mapper:

cat /etc/blkid.tab
UUID="4f05b919-fdf0-47c5-ae3c-d9541271883a" SEC_TYPE="ext3"
TYPE="ext2">/dev/hda1

/dev/hda2
UUID="fe6b1b62-a354-4041-809e-93ab8c74d4ce"
TYPE="ext2">/dev/hdc1

UUID="fe6b1b62-a354-4041-809e-93ab8c74d4ce"
TYPE="ext2">/dev/mapper/lsi_dafidifbfcb1


/dev/mapper will be present if dmraid is loaded. Unfortunately I fixed
the configuration before getting a snapshot of its contents.

The smoking gun is the "dm" entries in "/proc/partitions".

Cheers,
Jim