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spraguga Author

Level 1

63 points

OS Recovery Chunk Validation Failed - Possible Fix!

Hello All,

I have been troubleshooting the OS Recovery chunk validation failure for 3 days now and just found the weirdest fix. This might not work for you due to firewall or proxy issues but the steps below resolved it for me. So please feel free to try.

Mac Mini OS X Server 10.8.2

1. Boot from an OS Recovery drive or thumb drive.

2. Run the OS X Installer.

3. Open the Log Window.

4. Click the Save icon in the log window while the installer is running. This will error out the installer and show your current log. You will get a pinwheel for a minute but it will go away once the log saves.

- if I don't do this step I will keep getting "Chunk validation failed, retrying..." and chunk data never downloads and keeps retrying.

5. Now if I run the OS X Installer again the validation failure never comes up and chunk data starts copying as normal.

I have tested this about 3 times and it works for me. What a strange bug!!!

Hopefully this will help someone!

Thanks! 😉

Support all Mac machines, Mac OS X (10.5.7)

Posted on Jan 8, 2013 2:50 PM

Best reply

curious mike

Level 1

8 points

Posted on Aug 23, 2013 2:48 PM

I had this problem as well - with an Air at work...wasn't aware what was going on until I realized there was a log window under the windows menu.

I tried 3 successive times to complete the download using the "high speed" office connectionwireless once-ethernet twice] at work ranging from 4.5 hours to 6 hours and all failed with the "chunk validation" error. Local tech support didn't engage writing it off as "an Apple problem". I proposed that it was more likely to do with throttling and security settings on the firewall - both were rejected as implausible.

I took the unit home, replicated the steps from my 3 previous tries and 45 minutes later I had a complete install.

The moral of the story is try another network if you can - preferably one set up with more attention to functionality and less to security paranoia. Best of luck - this can be a time-consuming frustrating one to wrestle with.

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OS Recovery Chunk Validation Failed - Possible Fix!