New OS with a already setup LVM
 

I have a Ubuntu box which crashed last week "I shut down but never came back up". It has 3 hard drives which use LVM and another separate hd just for the OS

I really am worried about losing the data on the LVM. If I reinstall ubuntu will I be able to access the lv group with all its data? and how would I do this?

Not an LVM user but I would do the following. Remove the 3 hardrives and make notes to which cable they are connected to for reinstall later. Now I assume the one that is the OS is the master drive on the primary IDE or Sata channel. If so you may need to set the jumpers on that drive to be single drive status. Now boot up with a Live CD like Knoppix or Kubuntu. Once up mount the drive partition that contains the /etc/fstab file. Copy it down or print it out or save to a floppy or CD. If hand copy be exact. Best thing is copy to floppy or media stick or something.

Once that is backed up you can then do a reinstall and if possible selct upgrade or something like that. Not sure if Ubuntu has that option. If you must blank then go ahead. Now once the system is back up. Reinstall the drives. Set jumper on the master drive if changed earlier. Now but Ubuntu and open both the /etc/fstab on the new Ubuntu install and the backup copy. Cut and paste from the backup to the new install the lines pretaining to the LVM drive partitions.

I think this should work but not 100 percent sure. I would research this further or maybe someone here can say it would work.

Brian