On Mon, Dec 03, 2012 at 12:34:06AM -0700, Chris Murphy wrote: > 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, otherwise you might have a stale btrfs filesystem recognized inside the new filesystem. > However, the man page says -A, --alloc-start specifies the offset to > the start of the file system, and that the default is zero. If the > default is zero, the file system starts immediately, which implies > those 64KB of zero aren't actually intended for a boot loader. The alloc start doesn't change the location of the super, just the preferred location for any blocks we allocate. The idea was to test huge drives without having to fill them with data. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
