Do WinRar verify the files that is being compressed?

[Drake Jest]

Im doing some archiving and i got some Image backups that needs to be archived. Its about 1TB worth and since these are full disk image backups i know that compressing them will significantly reduce their size because not all imaged disk were full. I actually got a 370 GB compressed file.

 

My question is after compressing is it guaranteed that the files in the compressed file didnt get corrupted, does WinRar verrify it while compressing? (or is that an option that i have to enable). If winrar doesnt are there other zip program that do verify it?

[Levent]

7 minutes ago, Drake Jest said:

Image backups

Images wont get compressed. You can selectively choose to verify if files are stored without corruption in winrar.

[mariushm]

Open the archive with Winrar or 7zip or other tools and use the TEST option in the menu ... it will verify that the archive is good.

 

Winrar has the option to add recovery information to archives - between 5 and 10% can be enough to recover an archive if a few bytes are corrupted in the archive.

Alternatively, you can use a tool to generate parity information, like for example QuickPAR : http://www.quickpar.org.uk/Download.htm

 

It can create separate files with parity information (that can be used to repair archives if they become corrupted ... but how many corrupted bytes can be recovered depends on percentage of parity data and luck)

 

btw ... if those are mechanical drives, it may be worth to DEFRAGMENT the drive first so that you'd have as much continuous empty space when done, which will compress well.

Tools like O&O Defrag have options to defrag and compact files (bunch them together, usually during regular defragmenting a few sectors are left empty between consecutive files to reduce fragmentation in case user edits the file and increases in size by a few KB only)

 

 

 

@Levent he's referring to disk images , hard drive / ssd images

[Drake Jest]

32 minutes ago, mariushm said:

Winrar has the option to add recovery information to archives - between 5 and 10% can be enough to recover an archive if a few bytes are corrupted in the archive.

Sooo this must be checked before compressing right? A shame will have to redo 5 hours of compressing, its alright though ill do it while im asleep
 

32 minutes ago, mariushm said:

btw ... if those are mechanical drives, it may be worth to DEFRAGMENT the drive first so that you'd have as much continuous empty space when done, which will compress well.

 

They were defragmented before the images were taken so no problem there.

 

 

32 minutes ago, mariushm said:

Open the archive with Winrar or 7zip or other tools and use the TEST option in the menu ... it will verify that the archive is good.

 

Winrar has the option to add recovery information to archives - between 5 and 10% can be enough to recover an archive if a few bytes are corrupted in the archive.

 

Since im going to recompress them anyway, got any more suggestions on what other winRar settings should i set? For example im seeing "Use BLAKE2 file checksum" and "Save identical files as reference"

[mariushm]

I would suggest using 7zip and 7z format  and maybe using volumes (like for example 10-50 GB files, but try to keep the total files under 100-200). Use par2 / QuickPAR for error recovery data, as you can have that error recovery data in multiple copies in different places - if you bundle error recovery with the archive, the error recovery data itself could be corrupted.

You can get much higher compression speed and you can compress using all cores.  May also want to trade some compression efficiency for speed... for example on my system with a 5800x , I get around 19 MB/s on Ultra preset, 29 MB/s on Maximum, 33 MB/s on Normal...   so maybe you don't want 2 times the compression time for maybe 5 GB less on a 400 GB archive.  ... at 19 MB/s a 1 TB drive would already take around 15 hours to compress. 

 

For comparison, the Winrar benchmark test reports 16 MB/s ... so 7zip for sure would be faster

 

If you insist on using WinRAR, don't use the latest versions, use one that's "stable", like maybe WinRAR 6.24 : https://www.rarlab.com/download.htm

 ( scroll down and it's there on the page under the beta version and localizations)

 

While it won't give you as good compression (maybe a few GB bigger archive on a 1 TB drive), I would check RAR4 version instead of RAR5 for better compatibility - you get slightly less compression because RAR4 is limited to a 4 MB dictionary while RAR5 format defaults to 32 MB.

 

some article about winrar error recovery and how well it works here : https://www.liamfoot.com/analysing-the-effectiveness-of-winrar-s-rar5-recovery-records#heading_1