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Topic: par2, should i use? (Read 16201 times) previous topic - next topic
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par2, should i use?

hello again!
could you recommend if i should use par2 (if this is the newest, best recovery thing) to add security to my rips?
is there a guide on this site (i couldn't find one)?
would i need to re-rip my cds and par2 each flac image?
also, if i back my collection up on dvds, or anything really, i have about 250+ dvds with data/media on them, how long do they last? atleast 20 years minimum?
and one more thing, i would want to store the par2 on the dvd if i put it with the flac + cue, since if the flac corrupts couldn't the par2 aswell?
is par2 worth it? i'm pretty 'paranoid' so..

thank you!!

par2, should i use?

Reply #1 –
Sounds like you should make a real backup if you are paranoid ;-)

par2 will only protect you from corruption, and they are not really suited for any music-file unless you never edit the tags.

par2 creates a set of files based on an amount of security that you set yourself. Say, you want to secure your files against 10% corruption, you create par2 files equal to 10% of the initial data. If some files are corrupted, you can recover this, but only if the corruption is less that 10%. par2 will not save you from losing your entire music collection, which is why I backup a seperate copy of my music (and as for the tags, I backup these seperately, so I can restore anything at any time).

Edit, disclaimer: I might not have researched properly, and I do not guarantee that the information I provided is correct, as i never used par myself. But please correct me if it's entirely wrong
Can't wait for a HD-AAC encoder :P

par2, should i use?

Reply #2 –
no it seems right.
but isn't par/par2 based on probability? like say you do 10%, surely if you have like 100 copies of the same file and you 10 (or 9, whatever)% corrupt them in different ways, so that everyone is different, surely it can't fix each one?
also, what i'm trying to get at via my last question, is dvd archiving/backing up secure, ie. how long will my dvds last if i keep them in a case with virtually no dust, i doubt moisture, and heat or scratches etc. i hope they would last atleast 10 years, saying that i burnt them well and it's nice media. is this true?
thank you, and thank you odyssey!

-edit. ahhh what do you mean a real back up?!?!

par2, should i use?

Reply #4 –
in short: for backups on writable CD/DVDs better use dvdisaster instead of par2.

PS: The wiki is misleading, when it says that an ecc file (RS01) needs to be error free (true) it suggests that this also applies to RS02 (false). You should use RS02 anyway in case you can put less than 4.7GB on a DVD, here the ECC is added at the end of the DVD image and it is error tolerant in itself. If that's not an option for example for existing DVD backups or full-sized DVD movies then create and backup the ecc files of these RS01'ed full-sized DVD rips on a RS02'ed DVDs.

par2, should i use?

Reply #6 –
wow thank you guys for all the help!!
but my dvds should last atleast 5-10 years, by the time they can be like on blu-ray or something? should they?

par2, should i use?

Reply #7 –
Quote from: joshuatm on
wow thank you guys for all the help!!
but my dvds should last atleast 5-10 years, by the time they can be like on blu-ray or something? should they?

A harddisk is cheaper and more reliable than optical media. Why not buy a sufficient drive w/USB to backup your entire collection and store it elsewhere?
Can't wait for a HD-AAC encoder :P

par2, should i use?

Reply #9 –
Quote from: Eli on
Quote from: odyssey on

Quote from: joshuatm on

wow thank you guys for all the help!!
but my dvds should last atleast 5-10 years, by the time they can be like on blu-ray or something? should they?

A harddisk is cheaper


That certainly is NOT true.

Oh really? Let's calc... I have 500GB music I'd like to backup. I can choose a 500GB HDD for ~$100, or I could buy 120 DVDR's for ~$65. That'll just about do it - This is without any use of par2 recovery data and burning of 120 discs!!! Go ahead if you want, but my time is worth much more than the $35 difference!
Can't wait for a HD-AAC encoder :P

par2, should i use?

Reply #11 –
last week from amazon uk, 100 sony dvd-r. £25. that's $50.
so like 4.7gb each, 470gb at under £30 or $60.
deal to me!
i also like the feeling of putting away a disc and writing the name on it, having a massive case with them all in etc..

par2, should i use?

Reply #12 –
Quote from: beto on
That may be true in the US. Not in other countries.

I converted prices from DKK to USD

Quote from: joshuatm on
last week from amazon uk, 100 sony dvd-r. £25. that's $50.
so like 4.7gb each, 470gb at under £30 or $60.
deal to me!
i also like the feeling of putting away a disc and writing the name on it, having a massive case with them all in etc..

If you - like me - once discovered how optical media degrade, you would probably not choose that as a reliable backup media. It's no fun seeing your old data cannot be read.
Can't wait for a HD-AAC encoder :P

par2, should i use?

Reply #13 –
I can easily find 100 DVD (good quality - verbatim,....) for ~$20 without any problem. That is  $0.20/disc or ~$0.05/GB. I could find a 500GB HD for about $80 (if lucky), thats ~$0.16/GB, or ~x3 as much as DVDs.

par2, should i use?

Reply #14 –
Quote from: joshuatm on
but isn't par/par2 based on probability?

par2 and dvdisaster are based on Reed Solomon codes, afaik.

Personally, I'd disrecommend the use of DVD-R for long term storage (> 5 years) of data because of the instabilty of the materials (organic dye) of media.

par2, should i use?

Reply #15 –
Quote from: odyssey on
par2 creates a set of files based on an amount of security that you set yourself. Say, you want to secure your files against 10% corruption, you create par2 files equal to 10% of the initial data.

par2 is based on Reed Solomon Codes. If you use 10% of parity data you can protect your files only from a corruption of up to 5% of data. If you want to protect you data against a loss of 10% you need to use at least 20% of parity data.
My personal opinion is that it doesn't make sense to use more than 25 to 30% of parity data because there is the probability that the entire media fails and it does make more sense to make two (or more) copies of the data.

par2, should i use?

Reply #16 –
hmmm. i guess i'll just stick to nero's verfication on burn to make sure the data was burned correctly, then cross my fingers until i get a blu ray burner!
thank you for all the information!

par2, should i use?

Reply #17 –
I discovered this program while following the links in a forum: http://www.ice-graphics.com/ICEECC/IndexE.html

It's called ICE ECC and it's supposed to be "better" than par2. I did some very limited tests and it did seem to be faster to use. Might be worth checking out.

par2, should i use?

Reply #18 –
Quote from: naturfreak on
If you use 10% of parity data you can protect your files only from a corruption of up to 5% of data.

No. 10% pars will restore data with up to 10% corruption (assuming pars are not affected)

Quote
Personally, I'd disrecommend the use of DVD-R for long term storage (> 5 years) of data because of the instabilty of the materials (organic dye) of media.

And what is your recommendation then?

par2, should i use?

Reply #19 –
Quote from: Vitecs on
...10% pars will restore data with up to 10% corruption (assuming pars are not affected)

Are you sure? Does par2 use erasure error correction?

Quote from: Vitecs on
Quote
Personally, I'd disrecommend the use of DVD-R for long term storage (> 5 years) of data because of the instabilty of the materials (organic dye) of media.

And what is your recommendation then?

Store the data redundant on hard disk drives.

par2, should i use?

Reply #20 –
Quote from: naturfreak on
Quote from: Vitecs on

...10% pars will restore data with up to 10% corruption (assuming pars are not affected)

Are you sure?

Well, when backing up to DVDR (4.3GiB) I first create 3.3GiB images just filled with the backup data and the rest (~1GiB) is then used for RS02 ECC. So dvdisaster's RS02 mode provides ~30% redundancy from ~25% of ECC. Also I think to remember when data size equals ECC size the redundancy level is 200% (which is the maximum for RS02, btw).

I don't know about par2, but since you can fine tune its block size and stuff like that, which can greatly affect the level of redundancy and processing time, it's not so easy to say the same thing about par2.

par2, should i use?

Reply #21 –
Quote from: joshuatm on
could you recommend if i should use par2 (if this is the newest, best recovery thing) to add security to my rips?

No, imho, however, my take on this is quite different than the advice I've found around here, so this may be a bit heretical. 

Now, to explain, let me start with two things that I've come to accept. One, manufactured CD's and DVDs do not degrade in the same way or at the same rate as burned media; in fact, as far as I know, they don't really 'degrade' at all. The only reason that my pressed media has become unuseable has been due to use, ie. scratches, in the info, or lower, side of the disc, which can sometimes be removed, however, the underlying pits and lands are metal protected by plastic and so they should last a very long time. Two, burnable media is not the same as pressed media, and the process of burning a disc simply does not produce an indefinitely stable, long term product. From what I understand, CDR and DVDR media can fail in as little as a few months, or may be readable for as long as they have been around, which is decades by now.  Sure, they might last, but to me, might is simply not good enough.

Therefore, my backup strategy is to preserve the condition of my originals. I do this by not using them. So, each and every time that I buy a CD or DVD, I copy it, and then, I only use the copy, thereby saving the original as a perfect master.

As far as backing up CDRs or DVDRs, I agree with the aforementioned HDD solution. I also have FLAC files archived on a RAID.

My advice, just forget about backing up anything to CDR or DVDR for the long term.

PS. I do use .par files, on my archived files, just in case my RAID should fail, in which case data recovery may be required.
Quis custodiet ipsos custodes?  ;~)

par2, should i use?

Reply #22 –
Quote from: odyssey on
A harddisk is cheaper and more reliable than optical media. Why not buy a sufficient drive w/USB to backup your entire collection and store it elsewhere?


Do you know of any objective tests that support this assertion? I don't know if it's correct or not, but probably due to personal experience I believe the opposite is true. An HDD, being a rather delicate electronic device, might decide one day to call it quits. Optical media might degrade, but hopefully it will do so gradually.

I'm yet to lose anything on optical media, while I did have a few crashed HDDs. Some stopped responding completely (although that didn't happen recently), others had more localized damage.

par2, should i use?

Reply #23 –
Quote from: sheh on
Do you know of any objective tests that support this assertion? I don't know if it's correct or not, but probably due to personal experience I believe the opposite is true. An HDD, being a rather delicate electronic device, might decide one day to call it quits. Optical media might degrade, but hopefully it will do so gradually.

I'm yet to lose anything on optical media, while I did have a few crashed HDDs. Some stopped responding completely (although that didn't happen recently), others had more localized damage.


Here the idea is to backup your data to HDs, unplug and store. Hopefully when you plug it back some years later to extract your data, the drive which remains almost new should work fine. (hopefully no pata/sata/future issues)

For DVDs, my vote goes to dvdisaster. This is a must, for anything you hope to read again in 3 years. Par2 is fine and all, but when problems occur, there is the problem on how to extract the non damaged data... This is not trivial and dvdisaster covers this. In fact, you might end using dvdisaster anyway to extract what you can and then hopefully apply the par2 check and recovery.

Letting dvdisaster manage both the redundancy creation/restore and the data extraction is better imo.

The way you work with dvdisaster is this: You burn the disc, use dvdisaster on it to create the redundancy (only if the disc is 100% readable) and the file is created and properly stored.

In 3 years when your disc has developed errors, you use dvdisaster with your stored redundancy file to extract what it can and repair and you are given a repaired image you can burn again.

They seem similar but par2 works with files in a working/mounted filesystem while dvdisaster works with images and the device directly. This really makes a difference when the worst occurs...
She is waiting in the air

par2, should i use?

Reply #24 –
Quote from: naturfreak on
Quote from: Vitecs on

...10% pars will restore data with up to 10% corruption (assuming pars are not affected)

Are you sure? Does par2 use erasure error correction?

From par2spec:
"The redundant data in the PAR files is computed using Reed-Solomon codes. These codes can take a set of equal-sized blocks of data and produce a number of same-sized recovery blocks. Then, given a subset of original data blocks and some recovery block, it is possible to reproduce the original data blocks. Reed-Solomon codes can do this recovery as long as the number of missing data blocks does not out number the recovery blocks."