Drive automatically deleting files when full normal?

[Everglow]

I have a Buffalo 1TB external hard drive that I only had for less that 3 weeks.
It became pretty full (like only 30GB remaining full)
Most of it is system back up and images (apparently around 550GB).
I was getting worried because I didn't know how to manage my ever growing amount of files but I found that it suddenly had 150GB free. It apparently managed to free over 100GB on its own, but shouldn't it have asked me first before deleting whatever files it deleted? (probably windows backup)
Just worried if this is a sign of a drive failing or if its perfectly normal as a measure to keep the drive working properly.

 

[jsmithepa]

Perfectly normal.

A failing drive doesn't delete files, it merely slows down, because it tries and tries.

Should it asked you? it solely depends, am guessing the backup App, how you had it configured.

 

[popatim]

Its perfectly normal for good backup software to automatically delete the oldest backup to make room for the newest. You should be able to turn off this feature if you wish but do you really want to micro-manage space on a backup drive?

 

[Everglow]

Ah, I see.
Thank you all for you time.