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What are "Input/output" errors, and how can I resolve them? |
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When copying to or from damaged media, or a disk with a damaged filesystem, CCC may report "Input/output" errors. If no other major errors are encountered, CCC will produce a dialog box indicating:
"CCC detected "Input/output" errors during the clone. These errors often indicate filesystem damage or hardware trouble with the source or target volume. Examine the CCC activity log to determine the nature of these errors and refer to the CCC documentation for additional advice on resolving this problem."
Correspondingly, the CCC.log file (read more about that at the top of this page) will list the files that CCC was attempting to read or write when the error occurred:
02:13:49 rsync: read errors mapping "/Applications/Keynote.app/Contents/Resources/Themes/Shared/flowers_h.jpg": Input/output error (5) 02:14:39 rsync: read errors mapping "/Applications/Keynote.app/Contents/Resources/Themes/Shared/flowers_h.jpg": Input/output error (5) 02:18:20 rsync: read errors mapping "Users/mike/Movies/1984.mov": Input/output error (5) 02:18:24 rsync: read errors mapping "Users/mike/Movies/1984.mov": Input/output error (5) 02:18:24 ERROR: Users/mike/Movies/1984.mov failed verification -- update discarded.
The exact errors may vary, and some may be duplicated. If the affected file path begins with a "/" and CCC reports a read error, it is probably your source volume (e.g. the boot volume) that is affected. Errors affecting the target volume often indicate that "mkdir" failed or other write errors occurred, or the path will indicate the name of target volume.
Occasionally these errors are reported because your filesystem is damaged, but these errors typically indicate that your hard drive is dying. You have a narrow window of opportunity to back up the data from that disk to another hard drive. Time is precious; components could fail at any moment rendering the drive completely unmountable. Read activity is stressful on a dying volume, especially a full-volume backup. When I run into these errors on a hard drive that has not been backed up, I immediately back up the files that are most important. Once the most important data is backed up, I then try to do a full-volume backup. Once all important data is backed up, I then may try a filesystem repair utility (e.g. Disk Utility or Disk Warrior) if signs of imminent faliure are not present (e.g. particulary noisy drive, or loud, repetitive clicks).
What if the dying drive's volume won't mount?
More often than not, you're completely out of luck. I provided tech support at a University many years ago and had the opportunity to witness many failed drives. Occasionally we were able to revive a hard drive for small amounts of time by letting the drive cool down (somewhere cool and dry, not cold) and then powering it up attached to a service workstation (e.g. don't attempt to boot from it, you may not have enough time). When a drive doesn't mount, it typically goes to the recycle center or to DriveSavers if the data is worth the recovery cost. If you're reading this paragraph now because you're in this situation, my heart goes out to you.