DNG File Sizes

I shoot nothing but RAW (excpet when we occassionally use the P&S) and I've been using LightRoom for several years now. For some reason, I have always just used the CR2 RAW files supplied by the camera. I just got a 7D, so I figured this would be a great time to start importing the files into LightRoom as DNG files. I've only played with a handful of files so far, but the first thing I noticed is that the files are much smaller (~20%). Is this normal?

Yes.

Video by Julianne Kost Adobe Evagelist.

It's normal unless you shoot in one of the "small" Raw formats (sRaw, mRaw). We've seen that they do not convert well to DNG (it creates a huge file) so you might want to avoid that problem!

Another thing to consider is your backup strategy. A lot of people keep DNG as their "workingfiles" but backup both the CR2 and the DNG. One reason for doing this is if you ever want to work in non-Adobe Raw processing software that doesn't "read" DNG. The classical example of this is DPP, which to me is a very nice quick converter so I keep it and use it for those types of things, although I'm a died-in-the wool LR (and occasionally Photoshop) user from way back. I actually don't use DNG, but if I did I'd still want access to the original CR2s.

Yes, they compress a little more. mRaw/sRaw files balloon up to huge files so you might as well shoot full raw if you convert to dng.