I have a serious disk problem. I installed FC5 and accepted the default disk partitioning - LVM. First time I've used it, and may be the last for a while. Too many eggs in one basket!

I was logged in and browsing, nowhere near root, when I decided to reboot. Massive errors related to read-only file system - files in /var could not be deleted, etc.

Now when I boot, the kernel is uncompressed:

Uncompressing Linux... Ok, booting the kernel.
Red Hat nash version 5.0.32 starting
Reading all physical volumes. This may take a while..

Found volume group "VolGroup00" using metadata type lvm2
2 logical volume(s) in volume group "VolGroup00" now active

EXT3-fs error (device dm-0): ext3_check_descriptors: Block bitmap for group 0 not in group (block 3925999616)!

EXT3-fs: group descriptors corrupted !
mount: error mounting /dev/root on /sysroot as ext3: Invalid argument
...

How do I recover?

i would just redo the partitioning if possible. Get a recovery disk like backtrack and boot it as a livecd. Then get a free harddrive and use backtrack to copy all your data on whatever drive you have that is ext-3. Then delete the partition,remake and fill with backup.

I'm not sure your problem is LVM. Actually I doubt that it is. You've got filesystem corruption for sure. But that in itself does not necessarily indict LVM - maybe, maybe not.

Did you do a normal reboot? i.e., a clean shutdown? Where you having problems before the reboot (why did you reboot?) Did you get those massive errors on shutdown? Sounds like you had a filesystem mounted readonly. That tends to happen when corruption is detected.

You need to manually run fsck on your filesystem(s). If you can't boot far enough to do that, you will need a LiveCD like Knoppix.

I had no indication of a problem when I decided to reboot. I don't remember just why I wanted to reboot, but /var was readonly on shutdown. As it happens, I had just read earlier today that a filesystem could be made readonly if disk problems were encountered...

The problem is a corrupt ext3 fs, not LVM. LVM just confused the issue.

I used Knoppix 5.0 to locate and activate the logical volumes, and have run e2fsck but it does not seem to be able to replace the missing block bitmap.