The context of that is: the default when the user does not specify.
If
the user chooses 'raid1' in the installer, they get 'raid1' for both
data and metadata.
This does not seem to be the case, and from what I can tell
Garry experienced this problem as well.
I tested this in a VM with two disks, I manually selected the "raid1" profile
with btrfs in the advanced custom partitioning screen. After the installation I ran
"btrfs filesystem df /", which output:
Data, RAID0: total=2.00GiB, used=1.54GiB
System, RAID1: total=8.00MiB, used=16.00KiB
Metadata, RAID1: total=1.00GiB, used=46.28MiB
GlobalReserve, single: total=4.39MiB, used=0.00B
I interpret "Data, RAID0" to mean that the data is striped rather than mirrored,
and thus my data will be lost if/when a single drive fails. I hope that I made some
obvious mistake, as this appears to be a pretty serious problem otherwise.