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Is it more reliable, faster, longer lasting to burn to CD/DVD a zip (or a few large zips) of files rather than the files as a folder?

Just thinking if 1000s of small files would not be as efficiently recorded compared with one or a few large zips.

Also, even after the burning program verifies the disc, I also use Beyond Compare to compare the files with those on the disc. Always binary compares as identical but I hear the drive stuttering presumably as the head is being shifted only slightly each time to seek the next file, which leads me to think that its best to make one or more zips and copy those locally to compare. Or is it that burning invidual files to the disc is not as readable which causes the head to stutter.

There aren't any problems, my disc burns are reliable, just thinking more of efficiency and longevity, the discs burn and verify fast enough on my 18x DVD burner.

I'm using ImgBurn mostly. Also used Nero in the past.

I burn whole discs closed, finalised. Not sure which write mode but would think Disc At Once from a temporary cached image made by the burning program would be the most reliable.

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4 Answers 4

up vote 10 down vote accepted

Zip would be more efficient. Not only because of compression, but because of how disks are laid out. Every file is a series of blocks. The last block may not be totally full. With a huge zip, you only have one 'last block', but as individual files, each would have a partially empty last block.

Safety wise, zips are more risky. If a single byte fails for an image, you'd probably never notice it. If a single byte fails on a zip, it may corrupt a huge chunk of files in the zip. Remember that optical media does degrade, and a clean burn now doesn't mean you'll never have problems in the future.

My personal call would be individual files. Not only a bit safer, but easier to browse individual files later. You'll forget what's on the disk, and browsing dirs and filenames easier than remembering what the hell 'backup 2010-12-15' actually.

EDIT: Efficiency of compression obviously depends on the files you're compressing. If the files are already compressed (image files, videos, docx files are already compressed) you'll get little additional compression. You'll still get the benefit of fewer "partially filled last blocks"

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+1 and accepted answer. I agree with individual files, no-one has said that individual files is less reliable. Convenience of individual files is an important point. Risk of more data loss with zips caused by damage vs individual files and the same damage weighs in favour of the individual files. Efficiency of storage is a low priority as you might agree, given the low cost of good blank DVD media. Speed of burning less data occupied by a zip is not important either given that this is a one off, and as you say may not compress with already compressed filetypes. –  therobyouknow Dec 7 '10 at 23:58
    
PS faster access of zip being smaller than uncompressed files is cancelled out by the inconvenience of browsing the zip, again zip compression may not offer much benefit if files already compressed. –  therobyouknow Dec 8 '10 at 0:00
    
Only benefit of zip I can see is for files with long file names that need to be retained or for deep path names. Path depth and filename length can exceed the ISO or UDF standards for DVD though some burning programs may relax this. But the relaxation may not be standardised itself and be inconsistent and unpredictable results with sharing with other people. At least the .zip standard (and its related formats, .7z, .rar, etc) can retain full path depth and filelength, probably useful for website dumps, source code build trees etc. where importance retaining these outweighs the inconvenience. –  therobyouknow Dec 8 '10 at 0:03
    
@Rob good point on the filename stuff. There are extensions to the ISO spec, but as extensions, aren't guaranteed. –  Rich Homolka Dec 8 '10 at 0:25
    
extensions: indeed apps arbitrarily relaxing them isn't always a standard. But UDF is a standard allows for deeper paths than ISO and longer filenames. If the archive to optical disc, e.g. DVD, needs to be read by machines running OSs earlier than XP then ISO is recommended as old as well as new can read this, use .zip for deep paths. However, given that these are a diminishing minority, UDF is recommended if unlikely that older machines need to read the archive, also avoiding inconvenience and the more damage sensitive .zip (as @Rich Homolka points out in accepted answer). –  therobyouknow Dec 12 '10 at 0:51

A single scratch on a disk can wipe out a text document, or a spreadsheet. If that scratch is on the part of a ZIP file, it can wipe out the entire zip, which could be hundreds of documents..

If you really want to zip them up, do it in smaller batches of folders to limit how many would be lost if the disk is damaged.

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+1 about vulnerability of zip file vs individual files –  therobyouknow Dec 7 '10 at 23:50

You might want to look into dvdisaster for error checking and recovery of your discs. It's designed with optical media in mind, and offers the ability to create error recovery data that can be used to rebuild complete, uncorrupted data in the event of a problem with your disc.

It operates in 2 main modes:

  1. Building error correction files from an existing (preferably freshly-burnt) disc or disc image (ISO). You'll have to store these somewhere else, but they can be used to both verify that the disc is still readable without error or recover data from a damaged disc.
  2. Modifying a disc image with ECC data before burning. All the data needed to check and recover damaged data is available on the disc. Of course, this means that you need to leave some space free on your disc to accommodate the ECC data, but if it was already available there's no additional loss there.
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+1 for the dvdisaster tool, worth bearing in mind if I'm ever in that unfortunate position! –  therobyouknow Dec 7 '10 at 23:50
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The point of dvdisaster is that you use it before you get into that position, so you can recover your data when it really matters. :-) –  afrazier Dec 8 '10 at 3:16
    
+1 for that key point @afrazier your ref to dvdisaster is very enlightening, particularly given the uncertainty regarding ageing of optical media i.e. the break down of the (sometimes organic) dyes and compounds. It's always been a concern of mine, I rely on DVD media for backup, but I also group these into a Blu-ray backup and hard disc backup and maybe some of the data goes to online storage or as part of an online service such as flickr or youtube. –  therobyouknow Dec 8 '10 at 10:02
    
dvdisaster would go some way to addressing concerns about using optical media as long term storage. Curiously, as an aside I believe the UK National Archives at Kew Gardens in Richmond Surrey/London use magnetic tape for storing data, as tape has been around for a lot longer than anything else and its characteristics are known more than optical media. –  therobyouknow Dec 8 '10 at 10:05
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Archival is a very nasty situation to be in. It's really difficult to just "put stuff on a shelf" and forget about it. Just dealing with the media itself, you have to have a method by which you can make sure it's readable and that you have hardware which you can load media into. Just because your shelf of QIC-120 tapes has been sitting in perfect storage doesn't mean you have a drive that can read them. Even if you did, do you have a PC to hook them to? And that's without getting into the problems of file formats and format conversion, if necessary. –  afrazier Dec 8 '10 at 13:59

Rich's answer covers most of the details regarding performance, but I'd like to clarify the points on reliability and longevity. Let's go ahead and break down the question into its component parts.

With regards to burning ZIPs, rather than individual files, to optical media:

Is it more reliable?

Yes and no. Less writes are being done for the ZIP file means there is less chance that there will be a failed write in the process. However, more of the data residing in a ZIP file may be corrupted by an incorrectly written bit than would have happened if the contained files were written individually. How these two factors interact with each other statistically, I don't know. Perhaps someone who's done (or found) some actual analysis and comparison on this can better answer this aspect.

Is it faster?

Yes, of course. When burning a disc, your system is only concerned with writing ones and zeroes - not what file format those ones and zeroes represent. Therefore, the fewer ones and zeroes there are to write, the less time it will take.

Is it longer lasting?

No. At best, ZIP files will survive on a disc no longer than any other files. It is the physical media that degrades - not the data itself. That said, it must here again be considered that more files can be corrupted by a single bit's failure in a ZIP file, than would happen if the files were individually written. So, the ZIP file is actually more susceptible to degradation and therefore would likely have a shorter usable lifetime. Also, physical damages to the disc would have a much greater impact on a ZIP file than it might on individual files.

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For the "more reliable" point, with a zip file suddenly a scratch flips the wrong bit and the entire archive becomes unusable, rather than just the damaged portion. –  Joel Coehoorn Dec 7 '10 at 20:12
    
@Joel Thanks. I was interpreting "more reliable" in terms of write performance, not long-term storage. The latter is addressed in "longer lasting", although I did miss the point of physical damages. –  Iszi Dec 7 '10 at 21:02
    
+1 for further detail on the metrics I asked for. If the zip occupied much less space on the disk than individual files then there is less chance of data being physically damaged, however balance that with the situation whereby the smaller zip is damaged - it will be more disastrous than individual files. So I also agree with you saying "yes and no". –  therobyouknow Dec 7 '10 at 23:54

protected by Ivo Flipse Dec 29 '10 at 9:40

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