(RFE) Create "duplicate metadata" (DUP) profile instead of single for added reliability (like Linux 5.15+ does)

[IlgazC]

I was checking the web about a chunk warning message and read that before the Linux 5.15, BTRFS created single metadata profile instead of double (the new default). I think double metadata would also help people recover from USB disconnects/BSOD errors more easily.

Currently, I converted the metadata profile using:
btrfs balance start -mconvert=DUP /mnt/wd
I have about 700MB of metadata on that 1TB disk with lots of files. It isn't really using too much space to be a space concern.

Suggestion: Create/convert DUP metadata instead of SINGLE while converting. If possible.

[maharmstone]

The reason hasn't been done yet is because, as you say, it's trivial to do with btrfs-progs after the fact.

I was checking the web about a chunk warning message and read that before the Linux 5.15, BTRFS created single metadata profile instead of double (the new default).

More specifically, mkfs.btrfs defaulted to being SINGLE for SSDs and DUP for everything else. This was because it was speculated that SSDs might do their own data duplication, and it was reversed because there wasn't much data supporting this view.