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#1 2004-09-09 15:16:14
- argab
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Isit possible to create a parity DVD-R from a set of DVD-Rs?
Hello, I am new here. <!-- s
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I have read a bit this DVD-forum, but I don't find the solution for my idea.
The idea is this:
I have burnt 5 DVDRs and I want to create a parity DVDR.
The 5 DVDRs are general data DVDRs.
My idea is to apply the bitwise XOR function to the 5 DVDRs,
and store the result on the parity disc.
DVD1 XOR DVD2 XOR DVD3 XOR DVD4 XOR DVD5 => PARITY DVD
This should be very fast. The data DVDs are read sequentially (RAW data).
And the resulting parity data would fit on one DVD.
If the "data discs" are of different lenght, the parity disc will be as long as the longest of the data discs. But it will still fit on one DVD.
Is this possible with available software?
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#2 2004-09-09 16:32:31
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":3asr2pc7 wrote:
Is this possible with available software?[/quote:3asr2pc7]
It is possible, but only if each DVD contains a single file that fills almost the entire disk (with a few KB spare).
All you need to do is to use a PAR1 program (such as FSRaid) and create a single PAR1 file (which will have the file extension of .P00). When PAR1 programs create a single recovery file, the result is the XOR of all of the source files (plus a small header containing checksums that allow you to verify the files).
I would however recommend that you do NOT use this technique. The problem is that if you have an error on two or more disks, then no matter how small the error is, you will not be able to repair.
Instead, you should use PAR2. I suggest you read the tutorials for PAR2 and QuickPar.
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#3 2004-09-09 20:39:35
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
It is possible, but only if each DVD contains a single file that fills almost the entire disk (with a few KB spare).
[/quote:3pdlfu7k]
Big constraint.
Not possible <!-- s--><img src="{SMILIES_PATH}/icon_sad.gif" alt="
I would however recommend that you do NOT use this technique. The problem is that if you have an error on two or more disks, then no matter how small the error is, you will not be able to repair.
[/quote:3pdlfu7k]
yes, I am aware of this. But the same applies for hard-disk based RAID5 systems. Isn't it? And I suppose the risk is quite low in RAID5.Offline
#4 2004-09-09 22:21:50
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":3hj07ru0 wrote:
yes, I am aware of this. But the same applies for hard-disk based RAID5 systems. Isn't it? And I suppose the risk is quite low in RAID5.[/quote:3hj07ru0]
Yes, Hard Disks are very reliable, so the simple XOR technique used in RAID 5 is sufficient. If you get a sector failure on one drive, the RAID controller will use the data on the other drives and reallocate the sector elsewhere on the array.
DVDs are another matter entirely. They do not last as long, and there is a much higher likelihood of damage on more than one disk, so using a better protection scheme is sensible.
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#5 2004-09-10 00:04:54
- tgh
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":1nr5dd96 wrote:
Hello, I am new here. <!-- s
I have read a bit this DVD-forum, but I don't find the solution for my idea.
The idea is this:
I have burnt 5 DVDRs and I want to create a parity DVDR.
The 5 DVDRs are general data DVDRs
... (snip) ...
Is this possible with available software?[/quote:1nr5dd96]
You can do this with QuickPar, probably easier then looking for an XOR tool. Or you can do the PAR1 style using FSRaid.
A. [b:1nr5dd96]FSRaid method (PAR1)[/b:1nr5dd96]
1. Using ISO Buster, rip the contents of the (5) discs to (5) ISO files.
2. Create a PAR set for those (5) discs, where each disk is considered a single block. Create [b:1nr5dd96]2[/b:1nr5dd96] recovery blocks (taking the total # of disks up to 7).
Downside is that if you have damage on 3+ disks (1 more then you have recovery blocks for) your data is a goner.
B. [b:1nr5dd96]QuickPar method (PAR2)[/b:1nr5dd96]
1. Rip the data to (5) ISO files as in the other method
2. Using QuickPar, create a recovery set for those (5) ISOs, probably with a block size of 8MB or 32MB, at around 40% redundancy (2 discs worth). If your largest ISO file has N blocks, try to create at least N*2 recovery blocks. That will let you recover up to 2 full missing or damaged discs.
The downside to the ISO-rip method is that to validate the discs, you need to rip them to the hard drive in the future and then copy off one of the PAR2 files from the recovery discs.
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#6 2004-09-10 00:13:21
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
DVDs are another matter entirely. They do not last as long, and there is a much higher likelihood of damage on more than one disk, so using a better protection scheme is sensible.[/quote:4uab2k5y]
OH! , I didn't know that DVDs were so bad.
In fact, I thought the contrary: that, once the recording is done well, the data will stay there for many years, as long as you don't scratch the disc.
The hard discs in contrast, they can die in a matter of seconds, and you lose all the data.
That is why I have recently purchased 2 burners: a NEC 2510 and a Pioneer 107D. (I like redundancy here too, hehehe).
But now I am confused.
Well, anyway, I am also educating myself on RAID 5 (storage review forums). Maybe I have to battle in both fronts.so using a better protection scheme is sensible.
[/quote:4uab2k5y]
mhhh, I am reluctant to use complicated parity schemes right now. At least for now, I want it simple and fast. Maybe in the future...
What about applying the simple XOR technique to the ISO images of the DVDs? (an ISO image contains the raw data, read sequentially, isn't it?).
I have read in this forum that this is not a good idea because the "parity file" will not fit into a DVD, due to overheads....
How large is the overhead in the XOR file? In principle, the XOR file would be just the XOR data, and thus, no overhead at all is needed...no??Offline
#7 2004-09-10 00:38:16
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
@tgh:
we are now getting closer. <!-- s
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I was thinking in something like Method A.
Will each recovery block fit in a single DVD?
I guess with a single recovery block is enough. I think it is really
difficult that 2 DVDs get damaged at the same time. I will scan all the discs periodically at high speed, so, I think, I will catch soon any degenerative proccess that could be cooking.
Well, for important data, I will use 2 recovery blocks <!-- s
--><img src="{SMILIES_PATH}/icon_biggrin.gif" alt="" title="Very Happy" /><!-- s -->
About Method B, I don't understand because I am a beginner. What is the difference? ***Guessing****... I see, you divide the ISOS into many blocks, and now you treat these blocks as if they were discs. Instead of 5 ISOs, now you have, say, 1000 blocks in total, and you treat them as 1000 discs. Now you create 400 parity blocks, and thus you are able to recover all the stuff even in the event of any 400 blocks being damaged.
Then, I see a big advantage on the Method B, because you can recover all the data even if all the 5 DVDs are damaged, as long as the number of total damaged blocks don't go above 400. E.g., you can have 4 discs damaged, each one with 100 damaged blocks, and you would still be able to recover everything. I.e, now the 400 damaged blocks may be scattered in any way through all the discs, not neccessarily concentrated in 2 DVDs, as is mandatory in method A.
Yes, sounds impressive indeed!!
The downside to the ISO-rip method is that to validate the discs, you need to rip them to the hard drive in the future and then copy off one of the PAR2 files from the recovery discs.[/quote:1eerf6o3]
I don't understand this. Is this Method A or B?
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#8 2004-09-10 00:55:36
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":2zb2pivr wrote:
About Method B, I don't understand because I am a beginner. What is the difference? ***Guessing****... I see, you divide the ISOS into many blocks, and now you treat these blocks as if they were discs. Instead of 5 ISOs, now you have, say, 1000 blocks in total, and you treat them as 1000 discs. Now you create 400 parity blocks, and thus you are able to recover all the stuff even in the event of any 400 blocks being damaged.[/quote:2zb2pivr]
This is exactly how PAR2 works.Then, I see a big advantage on the Method B, because you can recover all the data even if all the 5 DVDs are damaged, as long as the number of total damaged blocks don't go above 400....[/quote:2zb2pivr]
Exactly!The downside to the ISO-rip method is that to validate the discs, you need to rip them to the hard drive in the future and then copy off one of the PAR2 files from the recovery discs.[/quote:2zb2pivr]
I don't understand this. Is this Method A or B?[/quote:2zb2pivr]
Both. Since A and B require you to create the PAR2 files from ISO files, it can only repair ISO files. This means that in order to verify a DVD you have to rip it to create a fresh ISO, and then use the PAR2 files to verify the ISO. If the ISO shows damage, you repair it, and then burn a new DVD from the repaired ISO.Offline
#9 2004-09-10 01:02:58
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":x93ciuff wrote:
DVDs are another matter entirely. They do not last as long, and there is a much higher likelihood of damage on more than one disk, so using a better protection scheme is sensible.[/quote:x93ciuff]
OH! , I didn't know that DVDs were so bad.
In fact, I thought the contrary: that, once the recording is done well, the data will stay there for many years, as long as you don't scratch the disc.
The hard discs in contrast, they can die in a matter of seconds, and you lose all the data.[/quote:x93ciuff]
CDs and DVDs record information by means of a dye which changes colour slightly when a high intensity laser beam is used to "burn" data onto it. The change is actually a chemical change.
Unfortunately, it seems that this chemical change is reversible and it seems that after a certain amount of time, the data will fade. The timespan seems to depend greatly on the way the disks are stored (i.e. keep away from sunlight, store away from heat or humidity etc), and also on which dye is used. There are discussions of this problem on various web sites.
With regards to hard disks, they are more likely to suffer from a mechanical failure than that actual data on the disks fading. In the case of a mechanical failure, you can send the disk off to a speciallist recovery firm and they will read the data off of the disk for you.Offline
#10 2004-09-10 03:08:38
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
@PeterBClements:
Both. Since A and B require you to create the PAR2 files from ISO files, it can only repair ISO files. This means that in order to verify a DVD you have to rip it to create a fresh ISO, and then use the PAR2 files to verify the ISO. If the ISO shows damage, you repair it, and then burn a new DVD from the repaired ISO.[/quote:20m763es]
Wouldn't it be easier to simply verify the DVDs with Nero Scandisk? I don't know exactly how Scandisk works, but I guess, when you burn data on a DVD, redundancy is added to the "user data". Errors are normal in optical storage. The redundancy helps to correct the errors as long as they stay in normal levels.
When errors become too high, they can't be corrected, but still can be detected. So you can know that the data is wrong. There is no possibility of reading the bad data without knowing it.
Conclussion: Scandisc will be able to truly verify the disc.Unfortunately, it seems that this chemical change is reversible and it seems that after a certain amount of time, the data will fade. The timespan seems to depend greatly on the way the disks are stored (i.e. keep away from sunlight, store away from heat or humidity etc), and also on which dye is used. There are discussions of this problem on various web sites. [/quote:20m763es]
yes. But these chemical changes are slow, and there are several methods to monitor them. You can use K-probe, or CDSpeed-Transfer rate curves, or Nero-Scandisc.
You can run the tests at high speed to magnify the errors. And, in case you can't read a disc at high speeds, you can try slower speeds and different readers (drives).
Also note that Kprobe reports the RAW errors of the disc, without using the error correction mechanism. You can see how these errors grow even before they compromise the error-correction mechanism.
Conclussion: if you monitor your DVDs frequently, you can predict when they fail irreversibly. Then, you can make a copy before its too late.
I don't see a big danger on the chemical changes.
More dangerous are the scratches. These happen in a fraction of a second. And the disc will get uncorrectable errors. Scratches can be caused by a faulty DVD drive. It happened to me. A Sony DDU1612. By the time I realized, I had several scratches, and uncorrectable errors. I didn't hear any weird noise (DVD readers do weird noises all the time anyway).
So, it is very advisable to check the discs each time you get them out from the tray, specially if the drive is new, or you are using new software. In fact, this scratches happen to me only when running Nero-CDSpeed-Quality test in that particular DVD drive. No other software do this. No other drive do this. Maybe this drive is faulty, I don't know. I don't use it now.
Then:
To cover the possibility of scratches, adding parity is very interesting.
And, at the same time, the parity will also cover the possible damages by chemical changes.
There is still a question unanswered:
In "Method A", will each recovery block fit on a DVD?Offline
#11 2004-09-10 03:20:49
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":14kl94gb wrote:
There is still a question unanswered:
In "Method A", will each recovery block fit on a DVD?[/quote:14kl94gb]
A "raw" recovery block would fit on the DVD (since it is the size of the ISO files), but you never have "raw" recovery blocks, they are always encapsulated inside PAR2 files.
The PAR2 file includes extra information to allow you to verify the source files and also to verify the recovery block.
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#12 2004-09-10 04:16:59
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
The PAR2 file includes extra information to allow you to verify the source files and also to verify the recovery block.[/quote:3qc074dz]
how much overhead is that info? Maybe its not too much after all...
Anyway, in this case, we woudn't need this "veryfication info", because as I have said, we can verify the DVDs with Nero's-Scandisk. The DVD recording system already contains "extra information for verification".
Well, note that I am not 100% sure of this issue, but I think this how it goes.
Can this "verification info" be excluded? Is there an option for that?
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#13 2004-09-10 10:42:05
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":2f75re6i wrote:
The PAR2 file includes extra information to allow you to verify the source files and also to verify the recovery block.[/quote:2f75re6i]
how much overhead is that info? Maybe its not too much after all...[/quote:2f75re6i]
It depends on what settings you use when creating the PAR2 files, but at a minimum it could be as low as a few KB.Anyway, in this case, we woudn't need this "veryfication info", because as I have said, we can verify the DVDs with Nero's-Scandisk. The DVD recording system already contains "extra information for verification".
Well, note that I am not 100% sure of this issue, but I think this how it goes.[/quote:2f75re6i]
The verification data that is included in the way information is written to DVDs and CDs can only handle corruptions up to a certain maximum size, and most importantly: any corrections performed are local as well. A local glitch or damage that gets too large cannot be corrected.
With DVDs configured to store data rather than movies or music, the amount of verification and repair information is massively increased. e.g. a CD rated as having a capacity of 700MB for data storage can be used to store a move that is 800MB in size. The 100MB difference is extra verification and repair information. Unfortunately if you have a large amount of damage to a limited region of the disk, that extra 100MB of repair data will not be able to correct the damage. This failue is due to the fact that the verification and recovery data stored in one part of the disk cannot contribute towards repairing another part of the disk.
The great advantage of PAR2 is that no matter where the damage is, and no matter where the PAR2 data is: providing that the total amount of damage does not exceed the amount of PAR2 data, repair will be possible.Can this "verification info" be excluded? Is there an option for that?[/quote:2f75re6i]
No.Offline
#14 2004-09-10 12:51:48
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
I think I am not understanding this "verification" or "validation" thing.
What is the purpose of "validating" the whole set of data+parity?
1. To simply check that all the blocks are ok
2. or To check how many blocks are damaged, and thus, evaluate the repairability of the whole package.
If it is "1.", i.e., to check that all blocks are ok, then Nero-Scandisc will suffice to verify the data and parity discs. Of course, the "verification data" built-in in DVDs is inferior to PAR if you want to repair (correct) , but its enough if you want to simply verify.
If it is "2.", then Scandisc won't suffice. We will need QuickPar.
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#15 2004-09-10 13:19:58
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
Strictly speaking, as far as verification is concerned, all QuickPar needs to know is where the errors are. It doesn't really matter how this information is obtained.
As you have noted there are programs available that can detect the presence of both soft (where the built in error recovery is sufficient) and hard errors (where the error is not correctable).
Obviously QuickPar cannot detect soft errors, so if you wanted to create a fresh copy of a disk before a soft error became a hard error, then you would clearly have to use one of those program to detect the problem soft that you can make the new disk before you lose anything.
QuickPar is designed to deal with hard errors. In order to be able to carry out a repair, QuickPar obviously has to know exactly where all of the errors are (and by implication how many there are and if there are enough recovery blocks to cover that number of errors).
As noted about, to do the repair, it does not matter how the location of the errors is determined. PAR2 provides a means to find the error locations using the verification data provided within the PAR2 files.
QuickPar could potentially use error location information provided by one of the programs you referred to. In order to do that, those programs would need to be able to output a report in a format that QuickPar could easily read and understand. e.g. The file might be plain text with one line per file giving byte ranges within the file were errors have been detected.
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#16 2004-09-10 13:36:52
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
In order to be able to carry out a repair, QuickPar obviously has to know exactly where all of the errors are (and by implication how many there are and if there are enough recovery blocks to cover that number of errors).
[/quote:2n89mgmc]
Then, the "validation" is only required when you are going to do a repair, isn't it?
I was confused, because I thought the "validation" was merely to rutinely check that everything was ok.
For rutine checks, Nero-Scandisc is enough, isn't it?
As long as Scandisc is passed, this means that the discs have no bad blocks, and then, no repair is needed.
When Scandisc is not passed on a disc, then I will go to "validate" and then repair. And then, and only then, I will need to RIP the discs into ISO images.
Remember that all this validation confusion started here:The downside to the ISO-rip method is that to validate the discs, you need to rip them to the hard drive in the future and then copy off one of the PAR2 files from the recovery discs.[/quote:2n89mgmc]
This is a relative downside, because you just have to do the ripping at repair-time. Not very often I hope <!-- sOffline
#17 2004-09-10 13:46:07
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":3buter42 wrote:
Remember that all this validation confusion started here:
The downside to the ISO-rip method is that to validate the discs, you need to rip them to the hard drive in the future and then copy off one of the PAR2 files from the recovery discs.[/quote:3buter42]
This is a relative downside, because you just have to do the ripping at repair-time. Not very often I hope <!-- s
That comment was written on the assumption that no other method was available to carry out a pure verification of the disk.
NB of course, that even if ScanDisk does not detect any hard or soft errors, the data might still be bad. This would happen for example if something went wrong when the disk was originally created and the content of the disk was not read back and compared with the data on the HD (from which it was created).Offline
#18 2004-09-10 14:53:41
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
That comment was written on the assumption that no other method was available to carry out a pure verification of the disk. [/quote:eycj0r73]
thg, I am going to kick your ass <!-- s--><img src="{SMILIES_PATH}/icon_lol.gif" alt="
NB of course, that even if ScanDisk does not detect any hard or soft errors, the data might still be bad. This would happen for example if something went wrong when the disk was originally created and the content of the disk was not read back and compared with the data on the HD (from which it was created).[/quote:eycj0r73]
But I always let Nero verify after burning. This does a comparison of the DVD versus the Hard disk. <!-- sOffline
#19 2004-09-10 15:24:27
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":mc0vhq3e wrote:
But I always let Nero verify after burning. This does a comparison of the DVD versus the Hard disk. <!-- s
I always use the verify option in Nero when burning aswell, but I'm sure some people are "stupid" enough to skip that step (to save time).
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#20 2004-09-10 16:53:27
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
I always use the verify option in Nero when burning aswell, but I'm sure some people are "stupid" enough to skip that step (to save time).[/quote:1c7xfz68]
indeed!
Check out this thread. The general oppinion there is that Verify in Nero is a waste of time. In fact, very important members of that forum have that oppinion:
<!-- m --><a class="postlink" href="http://club.cdfreaks.com/showthread.php?t=101830">http://club.cdfreaks.com/showthread.php?t=101830</a><!-- m -->
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#21 2004-09-10 17:43:11
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
They seem to be confused between the notion of verifying that what is on the disk is readable and knowing that what is on the disk actually matches what was on your hard disk.
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#22 2004-09-10 22:11:32
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
Yes, both are different notions.
Very soon I realized of the importance of Verifying in Nero.
My first ever DVD burn got a verify error!! it was very strange, I am not sure what happened, but a small .txt file was truncated. This was detected by Nero-Verification, but not detected by other programs, because the .txt file had no errors. CRCs correct. The file was truncated possibly by Nero, and then burned correctly.
Conclussion: always Verify in Nero. <!-- s
--><img src="{SMILIES_PATH}/icon_wink.gif" alt="" title="Wink" /><!-- s -->
Ok, so, recopilating, this would be the strategy, using PAR2:
1. Burn the 5 data DVDs as always. Verify after each burn.
2. Rip these 5 DVDs into Hard Disc, with ISOBuster.
3. Generate PAR files, for these 5 ISO files, with 40% of redundancy. I guess 40% is overkill, considering that we will be able to detect the errors soon, using the tools mentioned before, and considering that PAR2 is very flexible allowing any distribution of errors in the discs. I guess 10% of redundancy is more than enough.
4. Burn the PAR files into a "PAR-DVD".
5. Maintenance: Run Nero-Scandisc periodically to catch any possible hard-error that might develop. The more often you run Scandisc, the lower the number of errors you will get the first time you get errors.
6. If you get errors with Scandisc, Rebuild the set immediately.
Well, now a question:
lets suppose that, after a rutine Scandisc, you find errors in your "PAR-DVD" and in several "data-DVDs".
Even worse, you can't read the PAR-DVD in Windows.
The only way to read it, is using ISO Buster.
Q: Is it possible to recover the intact PAR files from that ISO? (I assume the disc is only partially damaged, and some PAR files are intact).
**more ideas**
maybe, this idea of forming groups of 5 DVDs is not convenient, because for rebuilding a single DVD, you need to rip the entire set (5 DVDs, plus the PAR-DVD)
Maybe its better to apply the idea to each single DVD individually. For example, dedicate 4GB for data in a "first session", and then burn 400MB of PAR files in a second session. what do you think about this? Can the 2 sessions be ripped independently with ISO buster, yielding 2 separate ISOs? Just like having 2 separate discs?
Another idea would be to burn 4,4 GB data DVDs (i.e, full), and generate a pack of 400MB parity files independently for each DVD. And store this "parity pack" in a sepparate session of a "PAR-DVD". This PAR-DVD would have capacity for 11 sessions, that would contain 11 parity packs (the parity info for 11 data DVDs).
In other words: you have 11 data DVDs. You generate 400MB of PAR files for each one, independently. Total, 11 "packs of parity". And store these 11 "packs" in 11 sessions of a separate DVD. To rebuild a damaged DVD, you just need the damaged DVD, and the corresponding session of the PAR-DVD.
This "disc a disc" approach is less powerful than the "set of 5 DVDs" idea, but the repair would be much faster.
also, to generate parity files for a set of 5 DVDs must be very slow.
Maybe it is better to do it one at a time. Although probably the overall time is the same in both cases.
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#23 2004-09-10 22:21:55
- argab
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
sorry for so many questions, but here is another one. <!-- s --><img src="{SMILIES_PATH}/icon_wink.gif" alt="" title="Wink" /><!-- s -->
About parity generation time in PAR2.
It surely depends on the total size of the data being protected.
But is this relationship linear? Double data, double time?
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#24 2004-09-11 01:21:52
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":1r1y0u84 wrote:
Ok, so, recopilating, this would be the strategy, using PAR2:
1. Burn the 5 data DVDs as always. Verify after each burn.
2. Rip these 5 DVDs into Hard Disc, with ISOBuster.
3. Generate PAR files, for these 5 ISO files, with 40% of redundancy. I guess 40% is overkill, considering that we will be able to detect the errors soon, using the tools mentioned before, and considering that PAR2 is very flexible allowing any distribution of errors in the discs. I guess 10% of redundancy is more than enough.[/quote:1r1y0u84]
You might find it slighly quicker to do the following:
1. Have Nero create the 5 ISO files from your data files.
2. Create the PAR2 files from the ISOs.
3. Burn the ISOs verifying after each burn.
4. Burn the PAR2s (again verifying).lets suppose that, after a rutine Scandisc, you find errors in your "PAR-DVD" and in several "data-DVDs".
Even worse, you can't read the PAR-DVD in Windows.
The only way to read it, is using ISO Buster.
Q: Is it possible to recover the intact PAR files from that ISO? (I assume the disc is only partially damaged, and some PAR files are intact).[/quote:1r1y0u84]
No, it is not possible to recovery the intact PAR2 file, but it is possible to make use of any good recovery data.
What you do is take the ISO you created from the PAR-DVD and rename the the .ISO file so that it has a .PAR2 file extension instead. You can then open this .PAR2 file with QuickPar. QuickPar will find all of the recovery data and you can use it to repair the 5 data DVDs. Once the data DVDs have been repaired, you can create new undamaged PAR2 files and burn them to a new PAR-DVD.maybe, this idea of forming groups of 5 DVDs is not convenient, because for rebuilding a single DVD, you need to rip the entire set (5 DVDs, plus the PAR-DVD)
Maybe its better to apply the idea to each single DVD individually. For example, dedicate 4GB for data in a "first session", and then burn 400MB of PAR files in a second session. what do you think about this?[/quote:1r1y0u84]
This is exactly what I do.Can the 2 sessions be ripped independently with ISO buster, yielding 2 separate ISOs? Just like having 2 separate discs?[/quote:1r1y0u84]
This I don't know. I've never attempted it.
If you can only RIP the whole disk, then what you would then need to do make a duplicate copy of the ISO and rename one copy as a PAR2. I do have a utility program that will extract the PAR2 data from any file, but have not published it yet.Another idea would be to burn 4,4 GB data DVDs (i.e, full), and generate a pack of 400MB parity files independently for each DVD. And store this "parity pack" in a sepparate session of a "PAR-DVD". [/quote:1r1y0u84]
This would certainly work as well.
There are many ways of arranging the files.also, to generate parity files for a set of 5 DVDs must be very slow.
Maybe it is better to do it one at a time. Although probably the overall time is the same in both cases.[/quote:1r1y0u84]
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#25 2004-09-11 01:30:03
- PeterBClements
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Re: Isit possible to create a parity DVD-R from a set of DVD-Rs?
"argab":5p7anm5p wrote:
sorry for so many questions, but here is another one. <!-- s
About parity generation time in PAR2.
It surely depends on the total size of the data being protected.
But is this relationship linear? Double data, double time?[/quote:5p7anm5p]
The time to create PAR2 files is given by the following formula:
Time = (source_size^2 * redundancy) / (block_size * speed)
So, for 4GB of data, a redunancy level of 10%, a block size of 2MB, and a speed of 250MB/s, this gives:
Time = (4096^2 * 0.1) / (2 * 250) = 3355 seconds = 56 minutes.Offline