[dm-devel] max_sectors_kb limitations with VDO and dm-thin

[Mike Snitzer]

On Wed, Apr 24 2019 at  3:45pm -0400,
Mike Snitzer <snitzer at redhat.com> wrote:

> On Fri, Apr 19 2019 at 10:40am -0400,
> Ryan Norwood <ryan.p.norwood at gmail.com> wrote:
> 
> >    We have been using dm-thin layered above VDO and have noticed that our
> >    performance is not optimal for large sequential writes as max_sectors_kb
> >    and max_hw_sectors_kb for all thin devices are set to 4k due to the VDO
> >    layer beneath.
> >    This effectively eliminates the performance optimizations for sequential
> >    writes to skip both zeroing and COW overhead when a write fully overlaps a
> >    thin chunk as all bios are split into 4k which always be less than the 64k
> >    thin chunk minimum.
> >    Is this known behavior? Is there any way around this issue?
> 
> Are you creating the thin-pool to use a 4K thinp blocksize?  If not,
> I'll have to look to see why the block core's block limits stacking
> would impose these limits of the underlying data device.
> 
> >    We are using RHEL 7.5 with kernel 3.10.0-862.20.2.el7.x86_64.
> 
> OK, please let me know what the thin-pool's blocksize is.

Nevermind, I see you have done so in another portion of this thread.