Use BTRFS replace with luks encryption

Question

I have a failing hard disk drive, which contains a partition forming part of my root filesystem:

matt@ryzen3950 ~> btrfs device stats /dev/dm-2
[/dev/mapper/cryptsda1].write_io_errs    0
[/dev/mapper/cryptsda1].read_io_errs     0
[/dev/mapper/cryptsda1].flush_io_errs    0
[/dev/mapper/cryptsda1].corruption_errs  12
[/dev/mapper/cryptsda1].generation_errs  0

I have another storage device that I'd like to replace this one with. To do this, I first partitioned and encrypted my new drive:

matt@ryzen3950 ~> sudo parted /dev/sdd
(parted) mklabel gpt                                                      
(parted) mkpart primary btrfs 1MiB 100%                                   
(parted) quit                                                             

matt@ryzen3950 ~> sudo cryptsetup luksFormat /dev/sdd1
matt@ryzen3950 ~> sudo cryptsetup open --type luks /dev/sdd1 cryptsdd1

(I did not perform any mkfs on this)

Then, I attempted to perform btrfs replace (note, this filesystem is currently live):

sudo btrfs replace start /dev/mapper/cryptsda1 /dev/mapper/cryptsdd1 /

However, I get the error:

/dev/mapper/cryptsdd1 appears to contain a partition table (atari).
ERROR: use the -f option to force overwrite of /dev/mapper/cryptsdd1

This makes it sound like I should not have partitioned the drive first. Should I have done the following instead?

sudo btrfs replace start /dev/sda /devsdd /

If not, what's the correct way to do this?

Finally, what is <path> in btrfs replace? I believe it's the filesystem mount point (e.g., / on a live root filesystem). Is this correct?

I read the full btrfs-replace manpage as well as the btrfs wiki, but was not able to find the answers to my questions.

Answer 1

However, I get the error:

/dev/mapper/cryptsdd1 appears to contain a partition table (atari).
ERROR: use the -f option to force overwrite of /dev/mapper/cryptsdd1

Just run the btrfs command with -f as suggested or run wipefs -a /dev/mapper/cryptsdd1 first.

You are actually hitting a known issue in libblkid (already fixed with newest util-linux), library which is used for detecting filesystems on devices and most storage tools use it -- btrfs is using it here to make sure the device you are trying to use is empty so it can warn users to not remove an existing filesystem by accident. In this case libblkid wrongly thinks the newly created LUKS device contains atari partition table, this is a false positive it just thinks some random data is atari superblock.

This makes it sound like I should not have partitioned the drive first. Should I have done the following instead?

sudo btrfs replace start /dev/sda /devsdd /

Definitely not, btrfs only cares about the filesystem level, it doesn't "know" about the underlying partitions and LUKS devices, recreating those first is the right thing to do.

Finally, what is <path> in btrfs replace? I believe it's the filesystem mount point (e.g., / on a live root filesystem). Is this correct?

I'm not btrfs expert, but I think this is correct and the first version of your btrfs replace command looks ok to me. Definitely make a backup first.