Interesting! Didn't know about that. I'll probably just get another red one if I replace those green drives.

The most discouraging thing about upgrading a device like the Synology is that you don't gain the space you're adding. I have 3 3TB and one 4TB drive. If I replaced a 3TB drive with a 6TB drive next (for around $235 according to Amazon right now), I'd only get another ~1TB of space I'd only see real advantages on the second drive replacement. Oh well, so it goes. So far I'm only at 5TB of the 8TB available, so I have a while.