Unreliable with OS X, damage

It's a shame, it is lightweight, fast and integrated hardware encryption.
BUT, bought for Time Machine in combination with hardware encryption, regularly it is either ejected after days of functioning, or Time Machine does not work, because it can not create folder. He takes me to eject and subtract it.
Finding made in OS X Yosemite updates and firmware.
If we add the fact that this is my second, the first having released after a few hours, I must say that unfortunately, I do not Rasht.
This note is hard, but it is a hard drive, reliability is the first criterion, ahead of performance, functionality and lightness.