It’s really unfortunate the btrfs “raid” seems to behave that differently than what one would expect from raid device.

With the udev rules and policy settings in mdraid, it creates no need for “managing a degraded array”. If enabled, detatching and attaching back is a hot-plug non-issue. So maybe the btrfs could also be solved with just some udev rules hooking on device events.

Any questions can be posted to the Technical Help Forums (Installation)

https://en.opensuse.org/User:Tsu2/systemd-1#BTRFS

From one of the links in my above Wiki,
I haven’t yet found anything new, better or different for creating, modifying adding or replacing a disk or otherwise managing a degraded array than what is in the BTRFS Wiki
https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices

Yes, I agree there is a future for YaST module(s) that can simplify BTRFS RAID management beyond initial setup.

Will btrfs start duplicating files on a single remaining disk in a strange attempt to “maintain data redundancy”?

And will the filesystem automatically re-sync a working spinning hard drive, that has been removed or turned off, with an SSD say in a laptop, after the hard drive has been plugged in or turned on again?

That is that instead of provicing a rubust, redundant array of individual disks, it provides a “broken multi-disk setup” whenever a disk fails or gets replaced phyisically, which requires manual fixing.

Have you been able to automate this with auxiliary scripts?

Objective –
New Install Tumbleweed on BTRFS RAID 10 using VMWare Workstation 15

Obstacle 1
VMware does not support installing a new machine on more than one block device, so the most direct scenario is not possible. But, it means that another related scenario can now be explored, converting a default TW install from a BTRFS root fs on a single disk to a RAID10 on multiple disks after install.

Step 1 install TW latest with intention to use YaST Partitioner as much as possible.
Then add 4 empty virtual disks after install.

Obstacle 2
Found that YaST Partitioner cannot add block devices to the mounted root file system device.
Seems YaST can create a new PROFILE (RAID Level and device group) with anything that’s not root, without further investigation don’t know if it’s because root is mounted or it’s just root. Since I cannot expand/add to the existing BTRFS fs using YaST, what follows can be done only with BTRFS tools.

Step 2 (or Step 1 using BTRFS tools)
Display BTRFS on current system, note that “filesystem” can be abbreviated “fi”‘

btrfs fi show
Label: none uuid: 9caca3c8-8b24-4754-bc44-1d4dcdf0ec4f
Total devices 5 FS bytes used 3.93GiB
devid 1 size 18.62GiB used 5.02GiB path /dev/sda2
devid 2 size 20.00GiB used 0.00B path /dev/sdb
devid 3 size 20.00GiB used 0.00B path /dev/sdc
devid 4 size 20.00GiB used 0.00B path /dev/sdd
devid 5 size 20.00GiB used 0.00B path /dev/sde

Note that devid 1 has something on it from my early experimentation creating a btrfs filesystem without RAID, and is why I will have to use “-f” to force striping in the following command. Am skipping my attempt without forcing which threw a surprising “No space left on device” error (which of course isn’t true)

Step 3 Execute conversion to RAID10

btrfs balance start -dconvert=raid10 -mconvert=raid10 /
Done, had to relocate 9 out of 9 chunks

Step 4
Success! The following command verifies

btrfs fi df .
Data, RAID10: total=8.00GiB, used=3.78GiB
System, RAID10: total=64.00MiB, used=16.00KiB
Metadata, RAID10: total=5.00GiB, used=159.41MiB
GlobalReserve, single: total=16.00MiB, used=16.00KiB

In other words, despite the goal of Btrfs developers to include LVM and/or RAID capabilities at file system level so you can live without those other technologies, Btrfs is (still) not a full replacement and there may be situations in which the usage of the most mature LVM/RAID is preferred.

It depends on the use case, but as you mentioned, is probably worth a try and some experiments. We encourage to have fun with it!

If you want to go beyond the Btrfs capabilities offered by YaST (that are admittedly a very small subset of all what Btrfs can do), the official Btrfs wiki would be a good place to start. https://btrfs.wiki.kernel.org

Raid 5 and 6 are technically implemented in some of the tools offered by the distribution and they can be used. But you will have to use the native Btrfs tools to configure it, instead of YaST.

Those Btrfs RAID levels are not officially supported in SUSE Linux Enterprise, which means if you use them you are basically on your own. Of course, it’s also available in openSUSE Tumbleweed and Leap, but with the same level of stability (that is, use it at your own risk).

Although I have religiously avoided software RAID in favor of hardware, this sounds interesting enough to experiment with. Will be looking for full documentation on not just setup but management, breaking sets and recovery. And, possibly guidance on using dissimilar block devices and if there are limitations, particularly in numbers of spindles.