[pve-devel] [RFC PATCH 2/2] common: btrfs: lower minimum amount of disks for raid10 to 2

[Christoph Heiss]

On Fri Jan 10, 2025 at 6:00 PM CET, Daniel Kral wrote:
> As the installer allows single-disk RAID0 configurations and BTRFS
> allows to create a filesystem with the RAID10 profile with only two
> disks since kernel version 5.15 [0], lower the minimum amount of disks
> the installer requires for a BTRFS RAID10 setup.
>
> The motiviation for this is to allow users to create a BTRFS RAID10
> configuration even though they do not have the necessary disks ready at
> setup time itself without needing to convert the profile afterwards.

Thinking about it, it does not really makes that much sense to allow
users to create degraded RAIDs - that just asks for all sorts of
troubles down the road in my book.

ZFS does not allow it either (or supports it AFAIK), for a good reason.
So IMHO we should not allow it with Btrfs as well.

*Especially* since Btrfs allows one to later on add more devices to a
filesystem and rebalance it to different profiles, e.g. from a RAID1 to
a RAID10 using

# btrfs balance start -mconvert=raid10 -dconvert=raid10 <mountpoint>

`-d` and `-m` of course depending on whether you'd want data block
and/or metadata chunks to be rebalanced.