My external sd card keeps losing files I have a 16gb card which I have transferred a few videos and books onto, but after a few days on my Galaxy tab the files have disappeared. I have tried three different cards, using different types of files, but after a few days they are always gone. Any ideas?
Is this a SD card that you have used for a long time on other devices? Do you, or have you, done a lot of writing to it?

SD cards have a limited lifespan, so the less amount of writing you can do to it, the better. You might want to do a chkdsk on it to see if it finds any bad sectors. If you find any, that would be your culprit.

I've had SD cards last for about a year and then files start disappearing, etc. That's when I would use it for everything - as the main SD card (swapping it), which means a lot of writing as apps save their data, backing up nightly with Titanium Backup, saving photos, caching, etc.

Once I learned about the limited lifespan of SD cards, I finally retrained myself to not use it as the main SD card. Now, I do weekly backups, once a week and I only store my music on the SD card, and photos that I take with the camera. The latest SD card I have has now lasted over a year which is longer than the others before it.

Also, quality of SD cards is a given. Don't go for the cheaper, off-name brands. They don't last long. It's better to shell out a few extra bucks and get a name brand.