I am using an external harddrive on a longform project -- It's a G Raid with 4 terrabyte capacity. 3 Terrabytes are being used. Lately, it's been acting differently, in that the light on the front flickers on and off. It appears on the desktop ok, but is this unusual behavior a sign that it's about to go? Should we have a full backup of the drive? What would be a good external drive to use for a backup?
I would back that drive up right away. Look at the drives at MacSales, the Mercury Elite and elite pro series.
That g-drive might be suffering from a drive failure, or a power source issue. Not bad now but it is giving you warnings. Back up right away, then get the drive looked at. Might even just try another power cable to it to see if that's it.
Without having more information, that light serves 2 purposes, power on & drive activity light. So the flickering normally would mean drive activity (I'm near certain you already know this)
I have 2 of the older G-Raid models with e-sata. One originally had a 2TB capacity where within a year the light would completely go out for periods of time but the drive was still working. GTechnology said the whole drive would need to be replaced because they don't "service" drives, which I thought was ridiculous. He admitted he had seen this LED behavior before but had no explanation. I later came to the conclusion it's temperature related. The warmer it got the LED would would show this odd behavior.
Two years or so later though that 2TB drive started showing signs of failure. It was out of warranty and after doing a bit or research I discovered the same controller inside is the same for their 2TB & 4TB models. I ended up buying two 2TB WD Enterprise drives, taking it apart & swapping them out myself making it 4TB as well. So if you do end up having to replace them, it's not that difficult to do it yourself.
Btw, I discovered they had cheaper Hitachi Deskstar drives in the 2TB model instead of Ultrastar's like in their 4TB+ for some reason.