Re: Delta patch not working on incremental restores

On 05/08/2023 16:40, Minh Van Le wrote:
> Hello dar-support,

Hello Minh Van Le,

> 
> Delta patches do not appear to restore for incremental backups.
> 
> I have created 3 different files with the same filename ("abc") and 
> performed a full, differential and incremental backup of each file (each 
> time using the previous backup as reference):
> 
>          dar.exe -N -va --delta sig -c dar1 -g abc
>          dar.exe -N -va --delta sig -c dar2 -g abc -A dar1
>          dar.exe -N -va --delta sig -c dar3 -g abc -A dar2
> 
> When restoring the backups with:
> 
>          dar.exe -N -va -x dar1 -w
>          dar.exe -N -va -x dar2 -w
>          dar.exe -N -va -x dar3 -w
> 
> dar1 and dar2 restore as expected. However dar3 gives "Error while 
> restoring : File the patch is about to be applied to is not the expected 
> one, aborting the patch operation".
> 
> The dar man page says:
> 
>          Dar adds a second level of checksum, to detect data corruption 
> inside the archive
>          and to check that the file the delta patch is about to be 
> applied is the expected
>          base file, this reduces the risk of "collision" but does not 
> remove it completely.
> 
> I am wondering whether this collision detection is interfering with 
> restores ?

I could reproduce the problem, version 2.7.8 works well on that topic. 
thus, it seems a regression appeared in 2.7.9. Unfortunately the version 
2.7.8 is not able to read archive generated by 2.7.9 and following 
version due to this fix:

"fixing bug concerning the restoration in sequential read mode of a
  backup containing binary patches"

which is also probably the cause of the problem here.

if you use binary delta with several iteration (incremental, not just 
differential backup), you should consider your backup not be able to 
restore those files.

I need more time to investigate, there is still maybe a small chance to 
avoid having you to rebuild your backups done with 2.7.9, 2.7.10 and 
2.7.11. Though there is a risk on your backup restoration capability, 
I'll have to advertise about that.

Thank you for your feedback!

> 
> Please see the attached test script and logfile ("bash -x" output) for 
> reference.
> 

Thanks for that also!

Denis

>