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Old 2006-12-27, 19:05   Link #21
Jinto
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Join Date: Feb 2004
Location: Fürth (GER)
Age: 33
Quote:
Originally Posted by zoltan_hellhound View Post
hdd's data lasts longer error free

how will the files get errors on the hdd?
data on hdd is represented by magnetic fields. Basically the polarisation of a little area makes a 0 bit different from a 1 bit. Now what happens if such an areas polarisitation becomes weaker over time (think about differently polarized areas around it that force influence on the isolated area given enough time). This effect is even worse when neighbouring bit-areas are rewritten very often (thereby changing polarization of neighbouring areas often). The influence on a once written data bit is ever there, and one day polarization may be lost or is weakly changed to the opposit (drives that do strange reread noises on certain sectors -sounds like a periodical drrrd...drrrd...drrrd...drrrd... - have such issues already. Most of the time it can be identified correctly by rereading it, but its information is almost altered at this point. The data is then in a critical condition).

Quote:
Originally Posted by zoltan_hellhound View Post
and whats the point in saving on dvds, the best way would be to have to hdds ans make par2 files ans store the files on boath the hdds.that way the file could last forever...ore at least 50 years
The point was, a hdd is only then more secure/reliable then a DVD if it is used as a backup drive that is only read/written to occasionally/sometimes. So by burning a working copy to DVD, you avoid reading the hdd copy often in regular/normal use. Think about this way. You backup a file on hdd and DVD, lets say this was done error free... now you would use the DVD whenever you just want to review/reread the data for personal use, like watching a movie on DVD, looking for images on a imge DVD and so on. The hdd is never to be used for this. It only exists to create new DVD backups, if the DVD working copies become too old or errornous.

Quote:
Originally Posted by zoltan_hellhound View Post
and another thing what wil hapen if my video files do get corupt in time..is ther a way to fix corupt files like avi,mkv,ogm
What does fixing mean? Repairing them so you can watch the video, but there is a bad frame in it, or is it meant like completely reestoring each and every bit?

While repairing simple errors might work without additional information, repairing each and every bit requires additional data, and the more altered data there needs to be recovered the more additional data must be stored beforehand in order to recover bit errors later. (I told you about the correcting codes once)

If something really needs to be stored very reliable it is usually stored in a RAID array of disks (e.g. RAID 5) http://en.wikipedia.org/wiki/RAID
But it requires you to use
a) several disks that work as one (expensive)
b) RAID controller (maybe expensive - some build in on some motherboards)

if you had two hdds in a lets say RAID 5 array, then they are basically bond together. You cannot interchange drives of different RAID sets because two drives act as one.

Since RAID arrays are so expensive, I suggested the mirroring on hdd and DVD instead.
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Old 2006-12-28, 09:08   Link #22
zoltan_hellhound
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Join Date: Dec 2006
So how long will the data last if stored in a god way..

how long dose a real dvd (the ones that are printed..sold) last.

i mean if the data is alterd like you said (the 1and0) and the dameg the get frome being stored on a dvd fore example. if i store on a disc/dvd and the data is alterd/corupt witch it will be in time is it then possible to fix dem whit like par2

if a file (mkv avi) gets bad how will it show on the disc?
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Old 2006-12-28, 09:55   Link #23
zoltan_hellhound
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Join Date: Dec 2006
one more thing about dvd discs

if i sucsessfully burn the info to a disc and its a god burn.is the only way fore the data to get bad is if its exposed to sun and temperature and/ore its stored to long..am i right?

so if i just store them fore like 3 years and take good care of them (they are only going to be used ass store discs) and never play them

and if i get the data moved sucssesfully frome the burned disc to the computer ther would be no chans of the data being bad?
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Old 2006-12-28, 14:08   Link #24
Jinto
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Join Date: Feb 2004
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Quote:
Originally Posted by zoltan_hellhound View Post
So how long will the data last if stored in a god way..

how long dose a real dvd (the ones that are printed..sold) last.
Basically forever. However, if scratches are on the frontside surface (or worse backside) or if the layers separate from each other, then you can consider the data as lost (on such parts of the disc).

Quote:
Originally Posted by zoltan_hellhound View Post
i mean if the data is alterd like you said (the 1and0) and the dameg the get frome being stored on a dvd fore example. if i store on a disc/dvd and the data is alterd/corupt witch it will be in time is it then possible to fix dem whit like par2
If you have chosen the par2 files big enough, so that there is enough redundancy to recover all errors that occured since your last error check, then yes, you can recover/fix them. Given the par2 files are not altered themselves (and that will be a tricky precondition... how do you make such files not ageing?)

Quote:
Originally Posted by zoltan_hellhound View Post
if a file (mkv avi) gets bad how will it show on the disc?
Usually you will not notice minor errors while viewing the video, so e.g. bad blocks, which you can identify while viewing, often require the change of several bits in a row. The only way I can think of, is to safe a crc (or sha) file and check for data consistency regularily (maybe every year or so)

Quote:
Originally Posted by zoltan_hellhound View Post
one more thing about dvd discs

if i sucsessfully burn the info to a disc and its a god burn.is the only way fore the data to get bad is if its exposed to sun and temperature and/ore its stored to long..am i right?
Well yes, but don't forget the light of the laser that is reading the DVD out while you watch the movie... it is a lightsource too.

Quote:
Originally Posted by zoltan_hellhound View Post
so if i just store them fore like 3 years and take good care of them (they are only going to be used ass store discs) and never play them

and if i get the data moved sucssesfully frome the burned disc to the computer ther would be no chans of the data being bad?
Never ever say never . The chances are not high, but there is no 100% guarantee for the consistency of your data (100% cannot be achieved by any means, one can just minimize the risk).

Last edited by Jinto; 2006-12-28 at 14:21.
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Old 2006-12-28, 14:20   Link #25
zoltan_hellhound
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Join Date: Dec 2006
If you have chosen the par2 files big enough, so that there is enough redundancy to recover all errors that occured since your last error check, then yes, you can recover/fix them. Given the par2 files are not altered themselves (and that will be a tricky precondition... how do you make such files not ageing?)


by storing them i a human brain..... i will make it happen
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Old 2007-01-02, 21:49   Link #26
jjacobs2
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Join Date: Jan 2007
DVD's aren't nearly as unreliable as you make them sound. They have built in error correction and there's even free software like nero dvd/cd speed to scan for the number of errors in a dvd. The data should be fine until too many errors build up and this results in a crc error when you try to access that data on the dvd. If you use good quality media with decent dye your data can last a long time. Obviously it's impossible to promise a hundred years since dvd's haven't been around that long but if the aging tests are accurate that is possible. Even so they only need to last 5 years or so until bluray or something else is just as cheap and much bigger. The most important thing is to use quality media like verbatim or taiyo yuden. Also consider the cost: dvd's store about 12 gigs for a dollar and hd's store about 3 gigs for a dollar. You can make 2 sets of dvd's in case a file is corrupted and still store twice the data for the same price.

You asked if dvd's can lose data other ways, and the answer is yes. The data is stored on a layer of organic dye. Like all things organic, this dye will eventually degrade and the number of errors on the dvd will build up until the error correction cannot fix it. Anyway, if you plan to switch discs to a new format every 5 years or so when significant improvements are made, like bluray, then you don't have to worry about the lifespan of those discs as much.
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