I have 1Tb drive with LVM on it. Now I've installed another 1Tb hard drive. And I want to make RAID1 without losing data on the first disk. Is there any way to do that without backing up data and then restoring it? OS: Debian 5
Create a new RAID1 specifying your new disk device and "missing" for the second disk device. This will start up a degraded RAID1 which will be fully working. You can the configure LVM on the resulting md device and get it all working how you like, copy your data across onto it.
Once convinced that you have everything working just right, and have backups of your data just in case, blow away your old drive (unmount it,