I created a 4 drive RAID5 setup using mdadm and upgrading from 2TB drives to the new Hitachi 7200RPM 4TB drives. I can initially open my luks partition, but later can no longer access it.

I can no longer access my LUKS partition even tho I have the right passphrases. It was working and then at an unknown point in time loose access to LUKS. I've used the same procedures for upgrading from 500G to 1TB to 1.5TB to 2TB. After the first time this happened a week ago, I thought maybe there was some corruption so I added a 2nd Key as a backup. After the second time the LUKS became unaccessible, none of the keys worked.

I put LUKS on it using

cryptsetup -c aes -s 256 -y luksFormat /dev/md0

# cryptsetup luksOpen /dev/md0 md0_crypt
Enter LUKS passphrase: 
Enter LUKS passphrase: 
Enter LUKS passphrase: 
Command failed: No key available with this passphrase.

The first time this happened while I was upgrading to 4TB drives, I thought it was a fluke, and ultimately had to recover from backups. I went an used luksAddKey to add a 2nd key as a backup. It happened again and I tried both passphrases, and neither worked. The only thing I'm doing differently this time around is that I've upgraded to 4TB drives which use GPT instead of fdisk.

The last time I had to even reboot the box was over 2 years ago.

I'm using ubuntu-8.04-server with kernel 2.6.24-29 and upgraded to -2.6.24-31, but that didn't fix the problem.