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Using par2 on my lossless CD-R backups

Reply #25
Quote
Peter - thanks for that test.  I've seen similar results.

So you agree that the sweet spot should be:

(1) the highest multiple of 2048 that
(2) gives the highest efficiency rating for
(3) one file set

In your example, that would be a block size in the range of  188,416 -  514,048.  Does that look right to you?  The process time would be really quick and the number of recovery blocks would be low.  Would that still yield the optimal results?

There are several conflicting things you are trying to achieve when selecting a block size:

1) Getting as many recovery blocks as possible.

2) Getting as high an efficiency as possible.

3) Mimimizing the time to create.

I've just done another test with a similar set of files (but this time I've adjusted the redundancy to get as near as possible to 100MB of PAR2 files), and gathered a little more information:


Code: [Select]
block   redundancy  recovery  efficiency  compute
size                blocks                time

20,480  15.04%     4,675     91.2%       4h 11m
40,960  15.79%     2,455     95.8%       1h 57m
81,920  16.13%     1,255     97.8%          56m
122,880  16.21%       842     98.3%          37m
163,840  16.26%       634     98.6%          27m
204,800  16.28%       508     98.8%          22m
262,144  16.27%       397     98.8%          17m
393,216  16.23%       265     98.7%          11m
524,288  16.20%       199     98.4%           8m
786,432  16.18%       133     98.0%           6m
[/font]

As you can see, the increased efficiency lets you have a slightly higher redundancy setting, but recovery block count does drop off very rapidly when you increase the block size to the value necessary for the peak efficiency.

I would suggest that as long as you are within a few % of the peak efficiency, you are probably OK, and it may be more important to have a reasonably high recovery block count.

At some point in the future I will be working on features specific to VD/DVD usage and when I do that I will set things up so that instead of specifying the redundancy setting to use, you will specify how much free space you want to fill up.

Using par2 on my lossless CD-R backups

Reply #26
Thanks again Peter for your hard work on this and attention to detail.  It appears then that a compromise of settings that gives relatively good efficiency and high recovery block count is the way to go.  I think I now have a much better understanding of the relationships and how I should be preparing my file sets for archive on DVDR.  Thanks.

Daffy

Using par2 on my lossless CD-R backups

Reply #27
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This is the way i prefer to do it, but i am afraid it might cause problems. If a CD-R containing par2 filesets gets so many errors that windows can't read it, and that i have to create an ISO image of the disc, will i be able to use all of the filesets on the disc?

Garathor:

I just have to say I'm very confused by what you're trying to do here.  Why do you prefer to do it that way?  Is there some reason you actually want to go to so much extra work?

You're storing your APE files on CD-R's.  You're worried about the CD-R's becoming damaged, in which case you would have to create an ISO to attempt to repair it.  You are going through all your files album by album to make par2 recovery files.

So, why don't you simply make a par2 file for each ISO to begin with?  I was under the impression that's how everybody does it.  You seem to have figured out the major drawbacks to doing file-by-file par2 creation when you're trying to protect removable media, yet you say that's the way you prefer to do it?

Just put your albums on CD-R's and then make a par2 recovery file for each ISO.  If the disc becomes damaged, you extract, repair, and re-burn.  This will potentially save you countless headaches.

Using par2 on my lossless CD-R backups

Reply #28
So what settings would you recommend from backing up to DVD? Too many different tables without any definite guidelines for me to following

 
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