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Validating Backup Volumes is Essential, Right-After and Later Too!

re: data integrity

I had just made a Carbon Copy Cloner backup of two key volumes onto a single new backup volume. The volume had been newly-erased in Disk Utility.

As is my practice, I then ran data verification using IntegrityChecker Java. The drive froze and locked-up with anything trying to access it and could not be unmounted. Files could not be listed or viewed, etc. So I was forced to unplug it and replug it.

After it was remounted, I tried data verification again. This time no hang. But the messages were a little unusual, because WARN_INACCESSIBLE usually means file permissions errors, and that made no sense. I found that I could not open the files, 'cat' them in Terminal, or copy them. The files were toast.

WARN_INACCESSIBLE: /Volumes/TBS_Clone/_Master/WebSiteRequirements-materials/images/LLC_2765-HighContrast.jpg 
WARN_INACCESSIBLE: /Volumes/TBS_Clone/_Master/WebSiteRequirements-materials/images/Topology.gif
WARN_INACCESSIBLE: /Volumes/TBS_Clone/_Master/WebSiteRequirements-materials/images/ReidReviews-1.gif
WARN_INACCESSIBLE: /Volumes/TBS_Clone/_Master/WebSiteRequirements-materials/images/ReidReviews-3.gif
WARN_INACCESSIBLE: /Volumes/TBS_Clone/_Master/WebSiteRequirements-materials/images/ReidReviews-2.gif
WARN_INACCESSIBLE: /Volumes/TBS_Clone/_Master/WebSiteRequirements-materials/images/DirectoryStructure-overview.gif ...

At this point I wondered if the volume had been corrupted, so I ran Apple Disk Utility, which confirmed it. Take this to heart in your own backups:

  • If you don’t confirm that the data in a backup can all be read, you don’t have a confirmed backup.
  • If you don’t verify that the data is 100% readable and uncorrupted, you don’t have a confirmed backup.
  • Backups can be good today, and bad tomorrow.

IntegrityChecker saves your butt for all these situations, today, tomorrow, or a year from now.

Disk Utility: corrupted APFS volume
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