I just picked up a two drive NAS enclosure (Dlink DNS-323) and am looking for some suggestions for hard drives to install into it.
Is a "green" drive sufficient or will there be a performance hit? 32 or 64 mb buffer?
In general it depends a lot on what you're planning to do with your NAS, but given your choice of NAS, I don't think the drives will ever be the bottleneck, so you can buy pretty much what you like the most.
It's also worth pointing out that many "Green Drives" are not intended for 24/7 usage anyway.
If you get one of the most recent WD Caviar Green Power, you should be aware that they come set up with aggressive power management, so they tend to unload and load their heads quite frequently.
This might lead to premature failing. Several NAS manufacturers (e.g. Synology) are advising their customers to switch off this feature. For this you need a proprietary tool which only runs under DOS.
I'm working for years on Hitachi Deskstar disk drives with no flaw.
The only one that failed has run for 6 years 24/7... I consider this a nice MTBF (http://en.wikipedia.org/wiki/MTBF)