Re: raid1 root device with efi

[Forza <forza@tnonline.net>]

---- From: Matt Zagrabelny <mzagrabe@d.umn.edu> -- Sent: 2024-03-27 - 21:21 ----
> 
> Are folks using the "degraded" option in /etc/fstab or the grub mount
> options for the btrfs mount?
> 
> I've read online [0] that the degraded option can cause issues due to
> timeouts being exceeded.

No, i do not recommend it. The issue isn't with grub, but if a device is missing during boot (hotplug, cables, errors, etc), and the system continues to use the remaining disk and later the disk comes back online you would have a split-brain situation. As far as I know there is no specific handling in btrfs for this, and the recommended way is to wipefs a removed device before adding it back. 

For this reason it is better to be forced to manually handle the situation. You could, for example have a second boot entry for degraded mode, etc. 


> 
> Also, I'm seeing some confusing results of looking at the UUID of my disks:
> 
> root@achilles:~# blkid | grep /dev/sd
> /dev/sdb2: UUID="9a46a8ad-de37-48c0-ad96-2c54df42dd5a"
> UUID_SUB="7737fc5f-036d-4126-9d7c-f1726d550444" BLOCK_SIZE="4096"
> TYPE="btrfs" PARTUUID="3a22621c-a4e1-8641-aa0f-990a824fabf4"
> /dev/sdb1: UUID="BD42-AEB1" BLOCK_SIZE="512" TYPE="vfat"
> PARTUUID="43e432b1-6c68-4b5c-9c30-793fcc10a700"
> /dev/sda2: UUID="9a46a8ad-de37-48c0-ad96-2c54df42dd5a"
> UUID_SUB="9436f570-6d15-4c74-aff8-5bd85995d92d" BLOCK_SIZE="4096"
> TYPE="btrfs" PARTUUID="e3b4b268-99e8-4043-a879-acfc8318232b"
> /dev/sda1: UUID="BD42-AEB1" BLOCK_SIZE="512" TYPE="vfat"
> PARTUUID="02568ee9-db21-4d03-a898-3d1a106ecbec"
> 
> ...why does /dev/sdb2 show up in the following /dev/disk/by-uuid, but
> not /dev/sda2:
> 
> root@achilles:~# ls -alh /dev/disk/by-uuid/
> total 0
> drwxr-xr-x 2 root root  80 Mar 25 21:16 .
> drwxr-xr-x 7 root root 140 Mar 25 21:16 ..
> lrwxrwxrwx 1 root root  10 Mar 25 21:16
> 9a46a8ad-de37-48c0-ad96-2c54df42dd5a -> ../../sdb2
> lrwxrwxrwx 1 root root  10 Mar 25 21:16 BD42-AEB1 -> ../../sda1

I believe only the first device found can have a link. It is not possible to have multiple link from one UUID to several devices. 

> 
> What do folks think about the following fstab?
> 
> root@achilles:~# cat /etc/fstab

> #
> # <file system>                           <mount point>   <type>
> <options>                      <dump>  <pass>
> # / was on /dev/sda2 during installation
> UUID=9a46a8ad-de37-48c0-ad96-2c54df42dd5a /               btrfs
> defaults,degraded,subvol=@     0       0
> UUID=9a46a8ad-de37-48c0-ad96-2c54df42dd5a /home           btrfs
> defaults,degraded,subvol=@home 0       0
> # /boot/efi was on /dev/sda1 during installation
> UUID=BD42-AEB1                            /boot/efi       vfat
> umask=0077                     0       1
> 

I recommend you do not use degraded. Instead maybe you'd want noatime, unless you have strong reasons for using atime system-wide. The keyword "defaults" is  mostly a placeholder and isn't needed if you have other options. 

https://github.com/kdave/btrfs-progs/issues/377

~ Forza