Re: Unexpected raid1 behaviour

["Austin S. Hemmelgarn" <ahferroin7@gmail.com>]

On 2017-12-20 15:07, Chris Murphy wrote:
> On Wed, Dec 20, 2017 at 1:02 PM, Chris Murphy <lists@colorremedies.com> wrote:
>> On Wed, Dec 20, 2017 at 9:53 AM, Andrei Borzenkov <arvidjaar@gmail.com> wrote:
>>> 19.12.2017 22:47, Chris Murphy пишет:
>>>>
>>>>>
>>>>> BTW, doesn't SuSE use btrfs by default? Would you expect everyone using
>>>>> this distro to research every component used?
>>>>
>>>> As far as I'm aware, only Btrfs single device stuff is "supported".
>>>> The multiple device stuff is definitely not supported on openSUSE, but
>>>> I have no idea to what degree they support it with enterprise license,
>>>> no doubt that support must come with caveats.
>>>>
>>>
>>> I was rather surprised seeing RAID1 and RAID10 listed as supported in
>>> SLES 12.x release notes, especially as there is no support for
>>> multi-device btrfs in YaST and hence no way to even install on such
>>> filesystem.
>>
>> Haha. OK well I'm at a loss then. And they use systemd which is going
>> to run into the udev rule that prevents systemd from even attempting
>> to mount rootfs if one or more devices are missing. So I don't know
>> how it really gets supported. At the dracut prompt, manually mount
>> using -o degraded to /sysroot and then exit? I guess?
> 
> 
> There is an irony here:
> 
> YaST doesn't have Btrfs raid1 or raid10 options; and also won't do
> encrypted root with Btrfs either because YaST enforces LVM to do LUKS
> encryption for some weird reason; and it also enforces NOT putting
> Btrfs on LVM.
The 'LUKS must use LVM' thing is likely historical.  The BCP for using 
LUKS is that it's at the bottom level (so you leak absolutely nothing 
about how your storage stack is structured), and if that's the case you 
need something on top to support separate filesystems, which up until 
BTRFS came around has solely been LVM.

The 'No BTRFS on LVM' thing is likely for sanity reasons.  Using BTRFS 
on SuSE means allocating /boot and swap, and the entire rest of the disk 
is BTRFS.  They only support a single PV or a single BTRFS volume at the 
bottom level per-disk for /.
> 
> Meanwhile, Fedora/Red Hat's Anaconda installer has supported both of
> these use cases for something like 5 years (does support Btrfs raid1
> and raid10 layouts; and also supports Btrfs directly on dmcrypt
> without LVM) - with the caveat that it enforces /boot to be on ext4.
And this caveat is because for some reason Fedora has chosen not to 
integrate BTRFS support into their version of GRUB.