Re: Can't mount btrfs volume on rbd

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

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On 2015-07-21 22:01, Qu Wenruo wrote:
> Steve Dainard wrote on 2015/07/21 14:07 -0700:
>> I don't know if this has any bearing on the failure case, but the
>> filesystem that I sent an image of was only ever created, subvol
>> created, and mounted/unmounted several times. There was never any data
>> written to that mount point.
>>
> Subvol creation and rw mount is enough to trigger 2~3 transaction with
> DATA written into btrfs.
> As the first rw mount will create free space cache, which is counted as
> data.
>
> But without multiple mount instants, I really can't consider another
> method to destroy btrfs so badly but with all csum OK...
>
I know that a while back RBD had some intermittent issues with data 
corruption in the default configuration when the network isn't 
absolutely 100% reliable between all nodes (which for ceph means not 
only no packet loss, but also tight time synchronization between nodes 
and only very low network latency).

I also heard somewhere (can't remember exactly where though) of people 
having issues with ZFS on top of RBD.

The other thing to keep in mind is that Ceph does automatic background 
data scrubbing (including rewriting stuff it thinks is corrupted), so 
there is no guarantee that the data on the block device won't change 
suddenly without the FS on it doing anything.



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