OS X is reporting read or write errors on "Macintosh HD"

Have more than one kind of backup

A quick post about why it is good to have more than one kind of backup. This is the message I was greeted sorting out a client’s Time Machine backup this weekend. This Mac’s hard disk had certainly got a problem as the Time Machine backup had failed, so I had been looking into why. Further investigation showed File Vault had not completed encryption and was sticking part way through.

MacOS comes with a handy app called Disk Utility. It is useful for checking and repairing disks that have a problem. But it doesn’t always get it right. In this case Disk Utility gave the disk a clean bill of health. As I wanted to back-up the disk fast for my client I used Carbon Copy Cloner (CCC, and no I am not getting paid to promote this!), which did tell me what was going on, as shown in the screen shot above.

Fortunately CCC is pretty tolerant, so after clicking the proceed button I was able to save all the files as well as to create a bootable clone of the disk. If the disk had been in worse condition a backup would not have been so easy. I would have to have relied one of the earlier Time Machine backups that had succeeded, and used disk recovery software for the rest.

Further testing seems to indicate the read errors were not hardware, but the filesystem. No more errors were detected after fully restoring the system to a newly formatted Macintosh HD. However, the lesson is clear: have more than one kind of backup. Time Machine is brilliant, but won’t always work. Carbon Copy Cloner is also brilliant and I have been using it for years and it has saved many a situation for my clients.