I am trying to understand how btrfs works with Raid1.
Is it possible to create the filesystem with -m raid1 -d raid1 in which
there is only one device available when the filesystem is created. Is
it possible to refer to a second device as "missing"
The use case I am thinking of is converting an existing raid1 setup from
mdm + lvm + ext4 to btrfs with raid1 and subvolumes.
I would like to fail half of my existing mdm devices and re-initialise
them as btrfs. make subvolumes for each of my lvm logical volumes, copy
the data over, then remove mdm and lvm entirely and add back in the
devices that were supporting them as additional btrfs devices.
The problem I see is that, according to the wiki, specifying -m raid1
and -d raid1 with a single device causes two copies to be made on the
same device, whereas I really want it to start off degraded with only
one copy until I add in the second device. Trying to cram two copies on
the one device will make it run out of space.
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