btrfs-balance convert from raid1 to single on specific device?

[Robert Krig <robert.krig@render-wahnsinn.de>]

Hi,

I'm running Kernel 4.3 and Btrfs-tools 4.3 on Debian Jessie. I compiled
the tools and kernel myself.

Recently I added a new disk to my btrfs volume and wanted to proceed to
convert from single to raid1.
Unfortunately the new disk seems to be faulty and started throwing a lot
of errors.

The balance convert operation didn't manage to finish, and now I'm
trying to get my btrfs volume back to single mode so that I can mount it
read/write.

If I try to mount it degraded, then it complains that there are too few
devices to mount writeable. So it will only allow me to mount read-only.

So far, so bad.

I have managed to boot and mount the volume once, with the faulty disk
and cancel the balance operation.
Now I would like to convert it all to single again, so that I can
finally remove that faulty drive.

However, if I simply say
btrfs fi balance start -dconvert=single -mconvert=single /btrfs-volume

Wouldn't that theoretically move some blocks to the faulty drive? Can I
somehow specify to rebalance only the working drive?

I was thinking by specifying the device id, which seems possible
according to the manpage.
I just wanted to check with you guys first, if that should work as
expected, or will I run into further trouble?

Also, I understand -dconvert is for data, and -mconvert is for metadata,
but is -sconvert? Is that data and metadata combined, or are system
chunks something else entirely?

Thanks for your help.