OS X automatically deleting files Before I made multiple cloud accounts available to backup my Mac, running OS X El Capitan, I saved every file in All My Files onto a 16 GB external SD card.

I noticed that every few days everything on the SD card would seem to disappear.  Is there any explanation that could be had for this?
Backing up specific folders instead of copying the disk images (I realized that's what 'All My Files' consists of) has allowed me to make permanent backups with different services and devices, including my SD card.