Re: Btrfs warnings in kernel 4.13.5

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On Fri, Oct 13, 2017 at 12:02 PM, Duncan <1i5t5.duncan@xxxxxxx> wrote:
> Juan Orti Alcaine posted on Fri, 13 Oct 2017 10:40:20 +0200 as excerpted:
>
>> Hi,
>>
>> I've upgraded my system to Fedora 27 and now I see many btrfs warnings,
>> although the system seems to be working fine. Is this something I should
>> worry about?
>
>> # uname -a Linux xenon 4.13.5-300.fc27.x86_64 #1 SMP Thu Oct 5 16:57:11
>> UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
>>
>> # btrfs --version btrfs-progs v4.13.2
>
>> [  337.813416] ------------[ cut here ]------------
>> [  337.813453] WARNING: CPU: 5 PID: 459 at fs/btrfs/ctree.h:1559
>> btrfs_update_device+0x1be/0x1d0 [btrfs]
>
>> [  337.814256] ------------[ cut here ]------------
>> [  337.814281] WARNING: CPU: 5 PID: 459 at fs/btrfs/ctree.h:1559
>> btrfs_update_device+0x1be/0x1d0 [btrfs]
>
>> [  337.822161] ------------[ cut here ]------------
>> [  337.822185] WARNING: CPU: 5 PID: 459 at fs/btrfs/ctree.h:1559
>> btrfs_update_device+0x1be/0x1d0 [btrfs]
>
>> [  337.822868] ------------[ cut here ]------------
>> [  337.822890] WARNING: CPU: 5 PID: 459 at fs/btrfs/ctree.h:1559
>> btrfs_update_device+0x1be/0x1d0 [btrfs]
>
>
> Those warnings aren't anything to be /too/ worried about.  They are
> triggered when a btrfs device size isn't a multiple of the btrfs
> sectorsize (currently 4 KiB on amd64 aka x86_64).  You can manually
> shrink your btrfs devices the fraction to an exact 4 KiB multiple, or
> wait a bit, and a new release of btrfs-tools should have a command to do
> it for you.


So it's an open question now why it was created with a device size
that isn't divisible by 4KiB. Seems like a bad idea to make it easy to
create virtual block devices based on 512 byte divisions, as it makes
it easy to end up with unaligned sectors at some point if one of the
underlying devices is an AF 512e device. Was it manually created? Or
was it created via the OS installer? Some time ago there was a feature
proposal for the Fedora installer being able to create bcache and
dmcache devices, but I haven't seen anything yet.


-- 
Chris Murphy
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