BTRFS RAID1 array with 2 500 GB hdds, no errors. This is the root filesystem, so there are 3 partitions on each drive: 1 = /boot (ext4), 2 = / (btrfs), 3 (swap)
/boot is ext4 because upgrading the kernel does not always work if /boot was a btrfs filesystem (new kernel installed but grub config not updated).
Now, this mirror is moved to smaller drives, the new drives are 120 GB, so the btrfs filesystem has to be resized. Resizing both btrfs partitions can be done using GParted, for example. After resizing, the MBR with the partition information can be copied from the old 500 GB drives to the new 120 GB drives (
dd if=/dev/sda of=/dev/sdb bs=512 count=1), as well as the btrfs partition (
dd if=/dev/sda2 of=/dev/sdb2). (Ignoring the swap partition, which would have to be moved to fit within the 120 GB.)
Although the system boots and does not have a problem with the new 120 GB drives, one error message is being logged (dmesg):
BTRFS: couldn't get super buffer head for bytenr 274877906944
And a scrub finds a "super" error (but no data errors):
"error details: super=1"
Is there a risk of data corruption due to this error?
How can this be fixed?
Since 274877906944 is 256 GB, the old btrfs partition was >256 GB and the new one is <256 GB, it seems like the system is looking for the superblock at 256 GB?