I'm using FC4 with 4 drives in one lvm group. I just rebooted my system and got a kernel panic saying my lvm volume group was incomplete. I booted up Knoppix, and got this output when I try vgscan:

root@1[knoppix]# vgscan
Reading all physical volumes. This may take a while...
Couldn't find device with uuid 'j5thGA-PQgV-on7a-AYWh-5I0M-qFi9-WTO620'.
Couldn't find all physical volumes for volume group VolGroup00.
Couldn't find device with uuid 'j5thGA-PQgV-on7a-AYWh-5I0M-qFi9-WTO620'.
Couldn't find all physical volumes for volume group VolGroup00.
Volume group "VolGroup00" not found

However...

lvm> pvscan -u
Couldn't find device with uuid 'j5thGA-PQgV-on7a-AYWh-5I0M-qFi9-WTO620'.
Couldn't find device with uuid 'aZsnb5-YX3L-H6Mc-qAFd-N12V-tEHK-WLWFZ4'.
Couldn't find device with uuid 'j5thGA-PQgV-on7a-AYWh-5I0M-qFi9-WTO620'.
Couldn't find device with uuid 'aZsnb5-YX3L-H6Mc-qAFd-N12V-tEHK-WLWFZ4'.
PV /dev/hda2 with UUID ZfD31T-5T4p-Gf1k-PCve-bT41-KvrW-uXNpoD VG VolGroup00 lvm2 [114.38 GB / 0 free]
PV /dev/sda1 with UUID qwGzBA-rY7f-gHvw-yTgB-txRm-bMp5-glcjui VG VolGroup00 lvm2 [233.75 GB / 0 free]
PV unknown device with UUID j5thGA-PQgV-on7a-AYWh-5I0M-qFi9-WTO620 VG VolGroup00 lvm2 [6.69 GB / 6.69 GB free]
PV unknown device with UUID aZsnb5-YX3L-H6Mc-qAFd-N12V-tEHK-WLWFZ4 VG VolGroup00 lvm2 [215.69 GB / 215.69 GB free]
Total: 4 [570.50 GB] / in use: 4 [570.50 GB] / in no VG: 0 [0 ]
lvm>

It still sees my devices with the required UUIDs, it just won't mount them. I really just want to remove them from the volume group, mount the other two volumes, and take everything off of them. Is this at all possible?

Just curious: Why are the devices on which the last two PVs mounted "unknown?" I didn't realize that pvscan could even look at "unknown" devices.

The first is /dev/hdb1 and the second is hdb2.

Still curious Your answer tells us what they should be, not why they're showing up as "unknown."

What happens when you run fdisk -l?

I have a similar problem, pvscan -u returns:

Couldn't find device with uuid 'NYmSBn-Xnpb-69xE-wEs9-UP68-lQ4I-W2ypaM'.
Couldn't find device with uuid 'NYmSBn-Xnpb-69xE-wEs9-UP68-lQ4I-W2ypaM'.
Couldn't find device with uuid 'NYmSBn-Xnpb-69xE-wEs9-UP68-lQ4I-W2ypaM'.
Couldn't find device with uuid 'NYmSBn-Xnpb-69xE-wEs9-UP68-lQ4I-W2ypaM'.
PV /dev/sda5 with UUID 3bJATF-rfFh-pXnu-IMu4-RANh-1vd2-fgx1ON VG NAS lvm2 [9.12 GB / 9.12 GB free]
PV /dev/sdc1 with UUID jmCfsG-w5Si-tH1M-W5v8-UEdJ-KqZ1-ocxHLF VG NAS lvm2 [698.62 GB / 325.22 GB free]
PV unknown device with UUID NYmSBn-Xnpb-69xE-wEs9-UP68-lQ4I-W2ypaM VG NAS lvm2 [465.75 GB / 465.75 GB free]
PV /dev/sdb1 with UUID dM37BN-7Dk3-KQ2Z-MW9c-Y0yf-uC3h-Ytm5vp lvm2 [465.76 GB]
Total: 4 [1.60 TB] / in use: 3 [1.15 TB] / in no VG: 1 [465.76 GB]

fdisk -l returns:

Disk /dev/sda: 20.5 GB, 20524056064 bytes
255 heads, 63 sectors/track, 2495 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x9f979f97

Device Boot Start End Blocks Id System
/dev/sda1 * 1 25 200781 83 Linux
/dev/sda2 26 1045 8193150 83 Linux
/dev/sda3 1046 1300 2048287+ 82 Linux swap / Solaris
/dev/sda4 1301 2495 9598837+ 5 Extended
/dev/sda5 1301 2495 9598806 8e Linux LVM

Disk /dev/sdb: 500.1 GB, 500106780160 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00023d5f

Device Boot Start End Blocks Id System
/dev/sdb1 1 60802 488385527 8e Linux LVM

Disk /dev/sdc: 750.1 GB, 750156374016 bytes
255 heads, 63 sectors/track, 91201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00080009

Device Boot Start End Blocks Id System
/dev/sdc1 * 1 91201 732572001 8e Linux LVM

Disk /dev/dm-0: 400.9 GB, 400941907968 bytes
255 heads, 63 sectors/track, 48745 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000

Disk /dev/dm-0 doesn't contain a valid partition table

As for what went wrong? I removed /dev/sdb from the LVM and set it up as a normal ext2 to backup the data on the LVM, then re-installed Fedora 9.
I then recreated the LVM and copied across the data, so far no problems.

Then over several days, while doing other things I added /dev/sdb back to the LVM, seeing the total size of the LVM was not what I expected rather than resizing the LVM I partitioned the drive to add it to LVM, not realising it was already in LVM! There was my mistake, I think I just need to remove the UUID NYmSBn-Xnpb-69xE-wEs9-UP68-lQ4I-W2ypaM from LVM and it should start working again!

Any ideas??

The LV software assigns UUIDs to logical volumes. They're visible in /dev/disk/by_uuid, and managed in /etc/lvm/ in the backup and cache sub-directories.

When I copied a volume group (as part of a HD) using dd, I had to edit the backup/Fedora file before I could get vgcreate to assign a new UUID to the VG. (FYI: I name my VGs for the OS installed on them rather than using the default VolGroupnnn form. That's why I'm using "Fedora" in the preceding example.)

Editing fundamental control files in /etc/lvm should, obviously, not be attempted either casually or without a backup of anything you want to preserve. I only did it for a VG on the dd copy of the drive containing the VG, and only when the drive was mounted on a different computer using a different OS (Kubuntu) that did not normally even mount LVM volumes.

In other words, be careful and keep your backup safe.