grub2: btrfs: does not install core.img to boot block

[Gene Cumm]

Binary package hint: grub2

btrfs reserves the first 64kiB for boot loaders as its CoW (Copy-On-Write) features mean that a file may change logical blocks. This area may also be referred to as the "embed area", "embedded area" or "embedding area", depending on the context. core.img must be installed to this area to ensure that other files may be read appropriately.

This depends on (LP: #757446) which has already been fixed. A patch resolving this has seen some testing already.

[Colin Watson (cjwatson)]

Upstream decided that this was too risky for a 1.99 freeze exception, so I'm inclined to follow that and not try to stuff it into 11.04 either. We might consider this for an update later.

[Christian Reis (kiko)]

I'm curious about the impact of this bug, as I've been able to install grub2 and use it to boot a btrfs root partition configured as raid-1 just fine .

Does it mainly affect installations where btrfs is installed on the entire block device, with no partition table?

What about installations that put grub inside the actual partition (i.e. grub-install /dev/sda1)?

Is 64kb enough to hold the larger core.img files in, say, an LVM+RAID+btrfs setup as per bug 1059827?

[Gene Cumm (gene-cumm)]

I believe the primary use case would be when you wish to target the volume (i.e. grub-install /dev/sda1).

If the concern is size, this has been officially resolved with Boot Area B's specifications.

https://<email address hidden>/msg34016.html

  We do leave the first 1MB of each device alone. Can we do 256K-1024K
  for the boot loader? We don't have an immediate need for the extra
  space, but I'd like to reserve a little more than the extra 64KB.

With a small loader in Boot Area A and the primary payload in Boot Area B, this should alleviate most size constraints.

[Phillip Susi (psusi)]

This was fixed some time ago. Installing grub to a btrfs partition works fine in 14.04.