>Actually based on http://carfax.org.uk/btrfs-usage/index.html I
>would've expected 6 TB of usable space. Here I get 6.4 which is odd,
>but that only 1.5 TB is available is even stranger.
>
>Could anyone explain what I did wrong or why my expectations are wrong?
>
>Thank you in advance
I'd say df and the website calculate different things. In btrfs raid1 profile
stores exactly 2 copies of data, each copy is on separate device.
So by adding third drive, no matter how big, effective free space didn't expand
because btrfs still needs space on any one of other two drives to store second
half of each raid1 chunk stored on that third drive.
Basically:
Drive1 Drive2 Drive3
X X
X X
X X
Where X is a chunk of raid1 block group.
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