Question Winrar

[nandobadam]

If I have several 7z, zip and rar files and I compress them into a larger file in rar or 7z or zip format, if I use the "optimal" compression method, will the chance of a file being corrupted at some point increase compared to using the "Normal" compression method?

 

[londiste]

Yes and no.
From choosing "optimal" instead of "normal" - No. These compressions are all lossless and when uncompressed you get the exact same files back.
Compressing multiple files into one archive - a little bit. This is essentially because one file is easier to corrupt than several. The chances are low and you can mitigate by backups of course.

 

[nandobadam]

I have 4 HDDs where I store the same files

I thought that if I used the "optimal" compression method the chances of corruption during file compression and in the long term would be greater

For me, compressing several with Winrar already compressed files into a single large file (250GB) zip or rar or 7z is more organized and easy to transfer

 

[AusWolf]

Compressing multiple files into one archive - a little bit. This is essentially because one file is easier to corrupt than several. The chances are low and you can mitigate by backups of course.

This. I would never compress several files into one when archiving long-term. Losing one by pure chance is bad enough, losing all of them is a lot worse.

 

[Frick]

For me, compressing several with Winrar already compressed files into a single large file (250GB) zip or rar or 7z is more organized and easy to transfer

That's why we have folders.

 

[nandobadam]

corrupt 1 big file compacted is easy occurs in hdd 2.5" storage archival?

 

[AusWolf]

corrupt 1 big file compacted is easy occurs in hdd 2.5" storage archival?

That's not the question. The question is, if your compressed file gets corrupted, are you ready to lose all of its contents?

 

[nandobadam]

What are the possibilities to prevent this large compressed file from becoming corrupted?

 

[AusWolf]

What are the possibilities to prevent this large compressed file from becoming corrupted?

Don't bother with compression. If you have 100 files, and one gets corrupted, you can still use 99. If you compress those 100 files into a large .zip or .rar, and that large file gets corrupted, you'll lose all of its contents.

 

[nandobadam]

Managing multiple separate compressed files is a complex mess and if any file gets corrupted it is difficult to find out without analyzing them all, so I compressed them into a single file. In this case, is it important to have 4 HDDs with this file?

 

[AusWolf]

Managing multiple separate compressed files is a complex mess and if any file gets corrupted it is difficult to find out without analyzing them all, so I compressed them into a single file. In this case, is it important to have 4 HDDs with this file?

Why bother with compression at all? Can't you just organise your files into folders?

Let's say a single sector gets corrupted on each 4 of your drives. There's a pretty slim chance, but let's just suppose...
1. If you keep a single large compressed file copied over onto each of those drives, your data is lost (because the large file got corrupted on all 4 of the drives).
2. If you keep your files separate, then one single file got corrupted on each drive, which you can overwrite from the same file from another drive - no data is lost.

 

[nandobadam]

To have only one large compressed file and minimize the possibility of corruption of this file, what strategy should be adopted?

 

[AusWolf]

To have only one large compressed file and minimize the possibility of corruption of this file, what strategy should be adopted?

None. I do not recommend doing that at all.

 

[windwhirl]

To have only one large compressed file and minimize the possibility of corruption of this file, what strategy should be adopted?

As said before, it's preferable to have separate compressed archives instead of a single big archive. There just isn't a fail-proof strategy. And "fail-resistant" is subjective. Best that can be done relatively easy is to have multiple copies spread out on multiple disks in multiple places.

If you still insist on doing this anyway (and to be honest, even if you decide to keep your archives as separate files), you should make use of WinRAR's recovery record (unless something catastrophic happens, a 10 or 15% size should be enough, feel free to use more though). Do not enable solid compression for RAR files though. They make damage repair harder.

If you have no need for your 7z or ZIP files to be specifically 7z or ZIP archives, convert them all to RAR files and enable recovery record with all of them. Compression rate differences are negligible today anyway so, might as well switch to RAR that has better chances of being repaired if the archive gets damaged.

Compression of compressed files is usually pointless, so you can use any of the Store/Fastest/Fast compression methods anyway.

Considering you just want one big file, I doubt you're using multi-volume approach to this. But if you are, there's also a setting to create a number of recovery volumes in the Advanced tab. A single recovery volume can replace any lost/damaged volume, but only one. You can replace as many lost/damaged volumes as the number of recovery volumes you have.

With all that said, keep in mind interoperability requirements if you have them. For starters, current WinRAR versions (7.0+) use RAR 5.0 exclusively, and do not support making archives in the older and more well known RAR3 format. And specific characteristics, such as dictionary sizes beyond 1 GB or extreme path lengths (beyond 2047 characters) are only available through WinRAR 7.0 or later.

RAR3 files on Linux should be usable, but I have no idea what's the exact state of support for RAR5.0 files. Specially if your RAR files use characteristics that were just recently made available in WinRAR 7.0+.

Operating system compatibility with regards to Windows might also need to be considered. If you need support for 32-bit Windows, WinRAR is ditching it in upcoming version 7.10, with Windows Vista also no longer being supported (XP stopped being supported after 6.02 and Windows 2000 after 4.11). Self-extraction (SFX) modules are not affected by this however and should still work on 32-bit Windows as long as you specifically select the 32-bit SFX module.

 

[Bill_Bright]

I thought that if I used the "optimal" compression method the chances of corruption during file compression and in the long term would be greater

Technically speaking, you are correct. The greater the compression, the greater the risk the compression process causes corruption. But not by much. Compression in the first place poses the greatest risk. Additional compression just adds a little more risk.

Do note when you compress an already compressed file, you save very little space, if any. It is already compressed, after all. But note when you compress several compressed files together, there is a good chance you will end up with a single file that takes up MORE space than the individual files did. This is because the compression program has to create a new index/table for the new, combined file. So instead of 4 indexes, for example, from the original zipped files, now you still have the 4 indexes, plus a new index for the combined file. If I was set on doing this (and I'm not), I would unzip all the zipped files, then create a new zipped file, with only one index.

Either way, as AusWolf suggests, when you combine all these files into one, you are essentially putting all your eggs in one basket.

I personally don't like using compression programs at all, except, maybe, to make it easier to email a program, or temporarily store a program on a small flash drive so I can transport it to or from work. Even then it is more likely I would temporarily put the program out in the cloud instead of using compression - and I don't like the cloud either! I say that to point out how much I don't like using compression programs.

Hard disk space is cheap. I mean 24TB for $480! That's cheap! I would buy new drives, unzip all the files and store them on the new drives. That way, I won't have to worry about having a compatible unzip program in the future either. If $480 seems like a lot of money, then try to put a value on all that data you are trying to preserve, to include the value of all your time and effort to recover it, should your zipped files become corrupt.

 

[nandobadam]

I have a 150GB compressed rar file and inside it there are several zip, rar, 7z img files and some installers but I don't remember if I used the option to add recovery record

on that same HDD I have another 18GB rar file with several zip, 7z, rar files

and another 8GB file compressed in rar also with compressed files inside it

and some more uncompressed winrar and 7zip installation files

 

[windwhirl]

I don't remember if I used the option to add recovery record

Check the file properties. There should be a tab with the details (or just open the archive in WinRAR and use the Info button). If there's a recovery record, it will tell you how big it is. If there's no recovery record, it should say Absent/Not Present.

 

[DirtyDingusMcgee]

+1 for just don't compress them.

 

[Frick]

I have a 150GB compressed rar file and inside it there are several zip, rar, 7z img files and some installers but I don't remember if I used the option to add recovery record

Think of it this way: If any of that data is corrupted, all of those files are now corrupted. If you don't compress them, only one of the files is corrupted. There are mitigations (as the good windwhirl mentioned) but as the good Bill Bright mentioned (storage is cheap) there really is little point to this endevour these days. Especially if we're only talking hundreds of Gigabytes.

 

[nandobadam]

4,11GB is my recovery record total file rar 145GB


Does Winrar have any function to test for corruption in zip, rar, 7z files that are on the 2.5" HDD?