Handle broken disks with BTRFS

[vaschthestampede]

I'm testing the behavior of BTRFS in case of disk failure.

As a first test, I disconnect one of the two disks in "RAID 1".
I get errors whether it's boot disks or not, but the errors are different.
In case of boot disk I have this screen:


Otherwise I have:


How can I fix?

Ask if you need any other information.

 

[leesteken]

This has come up before on this forum. BTRFS will not mount a mirror when a disk is missing (and I really don't understand why they made this the default). You need to enable this option first. It's probably somewhere in the BTRFS documentation.

 

[Neobin]

Have a look here:

• https://forum.proxmox.com/threads/proxmox-wont-boot-with-degraded-btrfs-raid1.123990
• https://forum.proxmox.com/threads/s...ot-after-removing-one-disk.108223/post-465250

 

[vaschthestampede]

I followed this guide to temporarily change the GRUB.
The change was to add

rootflags=degraded

to the end of the line starting with linux.

This made it possible to overcome the problem of boot disks.
EDIT:
There is a strange thing, or rather (in my opinion) wrong.
Reported BTRFS volume capacity is twice the actual capacity.

For non-boot disks what should I do?

 

[vaschthestampede]

I think I've found a better solution.

In the screen initramfs insert:

mount -o degraded /dev/sda3 /root -t btrfs

Where "/dev/sda3" is the healthy disck.
And press Ctrl-D.

For non-boot disks in the proxmox shell enter:

mount -o degraded /dev/nvme0n1 /BTRFS

Where "/dev/nvme0n1" is the healthy disck, and /BTRFS is the mount path.

The problem of the reported BTRFS volume twice the actual capacity remains but, for me, seams more clear as solution.

 

[LnxBil]

There is a strange thing, or rather (in my opinion) wrong.
Reported BTRFS volume capacity is twice the actual capacity.

Yes, you'll also have this with ZFS. Due to compression, deduplication and other weirdness, you cannot say how big your virtual disk actually is, therefore the safer option was to just state what you have as a backing device. I don't like it either, yet here we are.

 

[Hemps40]

Any updates to this, I have a server offsite I cant ipmi into so to change grub id have to be local onsite , whats happens if I add rootflags=degraded even though both disks are working still?