Why simply updating MacOS can lose your data

11 March 2016 by Olivier Pavie

Several cases of data loss were seen on Apple devices when updating MacOS

As usual, before each update, the time machine utility on Mac creates a backup of your existing environment. Then we can think about the risks and anticipate the likely malfunctions.

A quick side note: on Mac, updates from Mac OS 10.6 are not supposed to generate data loss issues; an update keeps the desktop and all personal files intact.

The following explanations will be useful if your OS is new, to avoid data loss.

Different causes of data loss

Normally, data loss when updating an OS is caused by several recurring problems not necessarily linked to the type of computer, PC or Mac. These cases are mainly due to the hard drive or OS state during the update:

  • A drive with a corrupted files system (either because the drive is damaged or because it had many restarts because of a hardware problem) could be the cause of the problem. So a check of the drive before the update is necessary. On Mac, the SOS function of the drive utility which you can find on the Finder, in “Applications”, is available to deal with it. In case of an identified problem on the drive, you have to take the necessary measures before launching an update. It may be worthwhile running a SMART tool on your drive before the update in order to minimise the risk of updating to a corrupted drive.
  • Is it a major update or a qualitative update of the OS? System updates for bug correction are launched every day. These updates are important to do because bugs can cause compatibility problems from one version to another. On Mac, in the "Apple menu" > "Concerning this Mac", the software update button show the bowels of your Mac and applied updates, particularly on the OS.
  • The third major case is when there is not enough space on the hard drive: you increase the chances of losing everything during an update which would be nonetheless launched.

The cases of Mavericks and Boot Camp

Beyond the 10.6 version of macOS, common identified data loss cases on Mac during an OS update are generally in reference to Boot Camp and the Mavericks macOS 10.9 system.

  • Concerning Mavericks, most of the problems are solved by intermediate updates, like the 9.5 update which is the last so far. This one should be installed before you will update to a newer version, this way you are taking fewer risks of data loss.
  • Boot Camp allows you to use Windows on a Mac. The system splits the Mac drive into two partitions, one staying in MacOs mode with a HFS+ file system, the second is set up by Boot Camp using a NTFS file system, designed to be used by Windows. During an OS update, the risk is that the partition could be modified or erased,, especially with the 10.6 version. Before updating a Mac with an installed Windows on it, you should:
    • clone the drive,
    • create a backup of the users’ profiles of the Windows partition from Windows to an external drive, or a complete backup of Windows…

In this last case the recovery may be difficult, because in case, of Windows partition loss, you would have to reinstall Windows from Boot Camp and launch a restoration from this new installation. The best is so to create a real clone with suitable software like Winclone, knowing that Time Machine will not handle the Windows partition.  

Will updating a mac delete everything?

The short answer is not necessarily, but having a regular backup in place means that you limit the risk of losing valuable data. If you don't have backups in place, Mac data recovery software may be the answer for you.


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