About the 5% reserved ext4 space:
This is a default value. You can use another value by manually formatting the partition, using command line options.
From the man page:
Quote:
-m reserved-blocks-percentage
Specify the percentage of the filesystem blocks reserved for the super-user. This avoids fragmentation, and allows root-owned daemons, such as syslogd(8), to continue to function correctly after non-privileged processes are prevented from writing to the filesystem. The default percentage is 5%.
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I don't remember where I found years ago) that this can take a max value of 7% and a min of 1%.
You can use the tune2fs command to get back some or all of this space. It seems that it is more important for system drives.
About the Green / Blue drives:
I've bought Green WD drives as data drives, mostly 2TB. I only had a failure, and this (hopefully) before even partitioning the drive (so I did change it and took a new one). I liked the fact that they were silent and didn't get too hot. I tried a few Toshiba DT01ACA200 that went too hotter than Greens. Now, I buy Blue 4TB drives for this use, connected to a Sandberg 2-bay docking station.
Nevertheless, a friend of mine had 2 (or more?) WD Green failed in a Synology NAS system (2 units of 5 drives connected as a 10-disk unit). Half of the drives were another type (higher quality, I guess special for NAS use) and the remaining were Green ones. The drives worked as a RAID 5 group, so 2 failing drives mean that the entire 10-disk group is failing. This NAS was running 24/7 as it was used by a web forum, media server and a web radio playing 24/7. Perhaps this use was too much for the Green models, mostly used for mid or lower end PCs.