Choosing my own "file sequence" when burning DVD-R

October 4, 2006 12:54 PM

I'm archiving important data to a DVD-R. In addition to the important data, I'm burning recovery files (QuickPAR PARity files) to the DVD-R so that I can recover the data in case sections of the DVD-R surface are damaged. It would be smart to have my burning software (Nero) "interlace" the recovery files and the archival data across the surface of the DVD-R: (data file, PAR file, data, PAR, data, PAR, ...). How can I make Nero (or any other burning software) do this?
posted by Moistener to computers & internet (10 comments total)

You may be over-thinking this. In the time it will take get an answer to your question and setup your software, you could have burned three DVD-R copies.

Place each in a different, lightless container. Keep one on site, one at your house, and one in a safety deposit box or mailed to your mother.
posted by unixrat at 1:07 PM on October 4, 2006

The design of par and par2 means you only need to recover a certain number of blocks from either original data or recovery data. Once you get enough correct blocks from the media, you can recover your data. The order of blocks is not important. Thus you do not have to worry about interleaving them.

If you want added safety, generate more par blocks.
posted by clord at 1:41 PM on October 4, 2006

I agree that you're overthinking this. The whole point of par2 is that you can recover the data with any n out of m blocks. The "file" blocks are no more or less significant than the "par" blocks, the only thing that matters is that you can recover n blocks from the disk, it doesn't matter which.
posted by Rhomboid at 3:16 PM on October 4, 2006

Doesn't putting the PAR files next to the data they're for increase the chance you'll lose them both? I would have thought it was better just to have all the PAR files at the end.
posted by krisjohn at 3:36 PM on October 4, 2006

Hmmm... First I thought the OP was correct, it makes sense, then I realized that no matter what, if 20% of the total size is recovery data, if you lose 21% of the total data, you're screwed. So if it's interleaved and the outside 21% is scratched beyond repair, 80% of the lost data is actual data, and 20% is recovery...

Unfortunately, you're still left with fewer bits than the data originally contains. par recovery is a 1:1 operation, so you need to have at least an equal amount of bits as to when you started out.


Put this way, no matter what, if more than 20% of your disk is scratched, you're screwed. If less than 20%, then you can recover anything you need. (if you loose 15%, and it's all data, well, you have your par data to recover. If you lose 15% and it's all recovery, oh well... )
posted by hatsix at 5:16 PM on October 4, 2006

I could smell this logical mistake, but couldn't find it. Thank you.
posted by Moistener at 7:44 PM on October 4, 2006

You can change the priority of individual files in Nero (right click -> properties -> file priority), which should change the order in which it is burned. But, doing so is completely pointless...

All it takes is damage to the table of file entries or to the file entry for the root directory to render a dvd completely unreadable. Make multiple backup copies and don't forget to keep a copy or three offsite. (And if you want, put 100% PAR recovery volumes on another set of discs too.)
posted by yeoz at 7:50 PM on October 4, 2006

It seems like burning a disc full of PAR recovery files would be pointless if you can just burn another copy of the actual files. Why would you need the PAR files if you had multiple originals?
posted by odinsdream at 8:51 PM on October 4, 2006

It would probably be easier to burn the PARs on a separate disc. If you want to be able to safely recover from one bad disc, burn one PAR disc (for each set of data, maybe several discs total). To safely recover two, burn two discs of PARs (not the same PARs of course, but a PAR set big enough to be on two discs).

Sort of like a RAID array.
posted by neckro23 at 10:10 PM on October 4, 2006

But, again, if you're already burning a whole disc of the data, and another disc of PARs, why not just put two whole copies on each disc?
posted by odinsdream at 11:26 PM on October 12, 2006