Does rsync detect file corruption?

[Christian Hecht]

This can minimize the risk, but if you don't need the corrupted file  
actually, you can't detect that it is corrupted.

The corrupted file will be copied to a newer backup folder.

If you delete the old backups due to rotation, at any time the backup  
is worthless because it only contains the corrupted copy.

So some mechanism is needed to detect  corrupted files before copying  
to the backup.

Best regards
Christian

Am 24.05.2009 um 16:04 schrieb Mac User FR:

> A simple way to prevent this is to store the backup with a rotating  
> system and hard-linking files.
> You can do it with rsync --link-dest=DIR option and a post-exec  
> script that moves the backup dir to something like backup-200905241335
>
> In this way if the file got corrupted it won't be hard-linked and  
> you will have a safe copy from a previous backup. Hard-linking an  
> unchanged dir takes very few place.
>
> Best regards,
>
> Vitorio
>
> Le 24 mai 09 à 15:05, Christian Hecht a écrit :
>
>> This will safe you if your file is corrupted on the backup side.  
>> Rsync will copy it then again from the source because the checksum  
>> is different and everything is okay.
>>
>> But imagine the file is corrupted on the source side. Then rsync  
>> will copy the corrupted file again and if you delete older backups,  
>> at any time your backup is corrupted too.
>>
>> Someone pointed me to this case a few weeks ago, so i started  
>> thinking how to avoid this.
>>
>> I will try to write a tool which stores the rsync checksums ore  
>> generate own checksums for each source file.
>> Then, at any time the stored checksums can be compared with the  
>> source files.
>>
>> Best regards
>> Christian
>>
>> Am 22.05.2009 um 16:22 schrieb Daniel Carrera:
>>
>>> Matthias Schniedermeyer wrote:
>>>> Exactly.
>>>> But you can (periodically) add "-c", then rsync while checksum  
>>>> the whole content of all files.
>>>
>>> Thanks. I'll add a -c for the Saturday backup.
>>>
>>>> But IF you have (or suspect) such type of corrution, you have  
>>>> have an even greater problem: Your hardware is crap.
>>>
>>> Yeah. I hope I don't have that particular problem. But I want to  
>>> be prepared if it happens.
>>>
>>> Daniel.
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