DNG vs. ARW?

I don't know if anything is lost, but out of principle I would keep the original ARW/MRW. If you run out of space just burn them on a CD or DVD and store in a safe place. Better be safe then sorry I would think.

Thanks for the replies.

If there is doubt I'll stay with the ARW. However, lately I backuped my RAW files and I realized that I lost all the processing I already did. I know that there are smarter ways for backup without losing the processing, but I thought working with DNG can solve it.
I am working with LR so I can convert the files while importing them - no extra step.

A while ago, I was converting from ARW to DNG files since I liked the idea of a standard format. However, I found out that the dng conversion wasn't entirely lossless as the Sony metadata got lost -- in particular, the lens id is not preserved and one can no longer use programs like alphalensinfo to identify the lenses
note: the turns out the real story is more subtle -- see later in this thread

So, nowadays I just use ARW files. Also, I am a lot less worried about the file format becoming obsolete: first of all, there are excellent raw conversion tools that are in the public domain as ANSI C which will always work, and I can hardly imagine Adobe dropping support for raw conversion without giving a upgrade solution. Finally, since I wrote the alphalensinfo tool I now have more insight in the raw file format of Sony and it is a very straight forward TIFF file so it would be easy to support in the future if necessary.

Edited by Vivec - 20 July 2009 at 09:04

Thanks everyone!
Vivec, you abswered my question. I'll keep the ARW files (and maybe use the DNG for backup the original files, after the lensid is embedded).

At first blush storing the xmp info in the DNG file seems a good idea. However when you use a back-up program that only updates "changed files" (I have one of those and use it to make back-ups on external hard drives) it's much quicker backing up 4 or 5 kb xmp file updates vs. whole 9-30 MB DNG file updates (size depending on camera used).

So even w/o the problem pointed out by Vivec having small xmp files is not such a bad idea.

My workflow is actually a bit different:

I store all working MRW + ARW + XMP files on my internal hard drive.
Once a week I back up my entire raw file directory to an external hard drive, using the option "update changed files only".

In that way I have a back up with all the recent edits, even for files I shot 1 or 2 years ago and worked on the past week. This goes quite quickly since for the back-up of the edits the program only has to copy the updated xmp's, since the ARW/MRW's never change. Only new ARW/MRW's from that week have to get copied entirely. So if I would have converted everything to DNG's it would need much more time to back-up the much bigger files in case changes have been made to older files.

I still make a backup to DNG once or twice a year and burn those on DVD, but never re-back them up in case additional PP has taken place. That's kind of a "last resort" backup that has never been used yet.

pegelli: why bother with DNG in your annual DVD-burning session? Why not just burn the ARW+XMP files?

PS: please always use par2 on optical media intended for long-term storage.