I want to get an external RAID 0 or 5 hard drive array for backup only. I thought about 5400 RPM as less heat (and cheaper vs. a Seagate Barracuda).
I know the WD Green drives are not made/intended for RAID, but will there be any problem using these slower drives if the device is kept OFF/unplugged 99% of the time?
Or take no chances and just get drives made for RAID?
Raid 0/1 they will be fine. Raid 5 not so much. Depending on the actual ones you ended up with they may work, or may constantly drop out of the raid set due to tler. I have a set of WD Black drives that worked fine in Raid 5 until I had to rma one, the one I got back would not work and I ended up stuck with them not being able to use for my original purpose.
Some of these drives you can change the tler settings, some you can not. I would not bother with WD drives except for the RE series if you are trying to use them for another other then Raid 0/1. WD will just state you are out of luck if they don't work in any config other then that as no other configs are supported by them.
If you google WD Green drives and raid, you find loads of information about these issues.