Re: BTRFS messes up snapshot LV with origin

[Goffredo Baroncelli <kreijack@inwind.it>]

On 11/25/2014 09:29 PM, Zygo Blaxell wrote:
> On Tue, Nov 25, 2014 at 05:34:15PM +0100, Goffredo Baroncelli wrote:
>> On 11/23/2014 01:19 AM, Zygo Blaxell wrote:
>> [...]
>>> md-raid works as long as you specify the devices, and because it's always
>>> the lowest layer it can ignore LVs (snapshot or otherwise).  It's also
>>> not a particularly common use case, while making an LV snapshot of a
>>> filesystem is a typical use case.
>>
>> I fully agree; but you still consider a *multi-device* btrfs over lvm...
>> This is like a dm over lvm... which doesn't make sense at all (as you 
>> already wrote)
> 
> It makes sense for btrfs because btrfs can productively use LVs on
> different PVs (e.g. btrfs-raid1 on two LVs, one on each PV).  LVM is
> the bottom layer because not everything in the world is btrfs--things
> like ephemeral /tmp, boot, swap, and temporary backup copies of the btrfs
> (e.g.  before running btrfsck) have to live on the same physical drives
> as the btrfs filesystems.

Let me to summrize

1) btrfs-single-disk on lvm works fine
2) btrfs-w/multiple-disk on lvm works fine
3) btrfs-single-disk on lvm works fine even with snapshot

4) btrfs-w/multiple-disk doesn't work with lvm AND snapshot

However I still doesn't understood why you want btrfs-w/multiple disk over LVM ?



> 
>>>>> and mounting the filesystem fails at 3.  
>>>> Are you sure ?
>>>
>>> Yes, I'm sure.  I've had to replace filesystems destroyed this way.

In a previous email you wrote:
>> Multi-device btrfs fails at 2, 
So I assumed that the point 3 onwards were related to a "single-disk" btrfs.



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