Purpose of first 64KB of Btrfs partition

Solution 1:

No, Btrfs does not use this area for data. This is a bootloader area. Chris Mason, the principal Btrfs author, explained it in his answer to the following question (I added [few remarks] and code formatting for readability):

When creating a btrfs volume with mkfs.btrfs, I'm noticing that the first 64KB are completely blank. Is this gap expressly intended for installing a boot manager/loader? e.g. GRUB 2 allows installation of boot.img + core.img into a btrfs formatted partition, without using block lists (the --force flag). It appears to produce a bootable system.

Right, I wanted to leave room for bootloaders. I actually would have used a larger offset, but the other filesystem mkfs commands don't zero very far into the drive. I had to make sure that mkfs.foo would overwrite the btrfs super[block], otherwise you might have a stale btrfs filesystem recognized inside the new filesystem.

[…]

-chris [Mason]