On 2014-06-18 16:10, Chris Murphy wrote:
> 
> On Jun 18, 2014, at 1:29 PM, Daniel Cegiełka <daniel.cegielka@gmail.com> wrote:
> 
>> Hi,
>> I created btrfs directly to disk using such a scheme (no partitions):
>>
>> dd if=/dev/zero of=/dev/sda bs=4096
>> mkfs.btrfs -L dev_sda /dev/sda
>> mount /dev/sda /mnt
>>
>> cd /mnt
>> btrfs subvolume create __active
>> btrfs subvolume create __active/rootvol
>> btrfs subvolume create __active/usr
>> btrfs subvolume create __active/home
>> btrfs subvolume create __active/var
>> btrfs subvolume create __snapshots
>>
>> cd /
>> umount /mnt
>> mount -o subvol=__active/rootvol /dev/sda /mnt
>> mkdir /mnt/{usr,home,var}
>> mount -o subvol=__active/usr /dev/sda /mnt/usr
>> mount -o subvol=__active/home /dev/sda /mnt/home
>> mount -o subvol=__active/var /dev/sda /mnt/var
>>
>> # /etc/fstab
>> UID=ID    /    btrfs rw,relative,space_cache,subvol=__active/rootvol    0 0
>> UUID=ID    /usr    btrfs rw,relative,space_cache,subvol=__active/usr    0 0
>> UUID=ID    /home    btrfs rw,relative,space_cache,subvol=__active/home    0 0
>> UUID=ID    /var    btrfs rw,relative,space_cache,subvol=__active/var    0 0
> 
> rw and space_cache are redundant because they are default; and relative is not a valid mount option. All you need is subvol= 
> 
>> Everything works fine. Is such a solution is recommended? In my
>> opinion, the creation of the partitions seems to be completely
>> unnecessary if you can use btrfs.
> 
> It's firmware specific. Some BIOS firmwares will want to see a valid MBR partition map at LBA 0, not just boot code. Others only care to blindly execute the boot code which would be put in the Btrfs bootloader pad (64KB). I don't know if parted 3.1 recognizes partitionless disks with Btrfs though so it might slightly increase the risk that it's treated as something other than what it is.
> 
> For UEFI firmware, it would definitely need to be partitioned since an EFI System partition is required.
> 
> Chris Murphy--
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 
On most hardware, I would definitely suggest at least adding a minimal
sized partition table, the people who design the BIOS code on most
systems make too many assumptions to trust their code to work correctly.
 That said, I regularly use BTRFS on flat devices for the root
filesystems for Xen PV Guest systems, systems that boot from SAN, and
secondary disks on other systems with no issues whatsoever.