Re: LVM thinp, mkfs "device is not properly aligned"

[Dave Chinner <david@fromorbit.com>]

On Wed, Nov 15, 2017 at 04:20:59PM -0700, Chris Murphy wrote:
> # mkfs.xfs /dev/mapper/vg-timemachine
> warning: device is not properly aligned /dev/mapper/vg-timemachine
> Use -f to force usage of a misaligned device

That is emitted when blikid tells XFS that the device it is about to
format is not correctly aligned.

The check that is failing:

	 if (blkid_topology_get_alignment_offset(tp) != 0)

>From here:

https://www.kernel.org/pub/linux/utils/util-linux/v2.21/libblkid-docs/libblkid-Topology-information.html

ALIGNMENT_OFFSET: indicates how many bytes the beginning of the
device is offset from the disk's natural alignment.

....
> $ lsblk -t
> 
(Trimmed for brevity and readability)
.....
> NAME                      ALIGNMENT MIN-IO   OPT-IO
> sda                               0   4096        0
>   sda1                            0   4096        0
>   sda2                            0   4096        0
>     brick1                      512   4096        0
>   sda3                            0   4096        0
>   sda4                            0   4096        0
>   sda5                            0   4096        0
>     vg-cryptoswap               512   4096        0
>       swap                      512   4096        0
>     vg-thintastic_tmeta         512   4096        0
>       vg-thintastic-tpool       512 524288   524288
>         vg-thintastic           512 524288   524288
>         vg-timemachine          512 524288   524288
>     vg-thintastic_tdata         512   4096        0
>       vg-thintastic-tpool       512 524288   524288
>         vg-thintastic           512 524288   524288
>         vg-timemachine          512 524288   524288
> 

What you can see here is that all the volume groups have a non-zero
alignment - they are all off by one sector - and that's what
mkfs.xfs is warning you about. i.e. something's not quite right at
the LVM layer....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com