getting to 4K disk blocks in ZFS

[Ben Morrow]

Quoth Karl Denninger <karl at denninger.net>:
> On 9/11/2014 1:24 AM, Andriy Gapon wrote:
> > On 11/09/2014 04:22, Steven Hartland wrote:
> >> ----- Original Message ----- From: "Aristedes Maniatis" <ari at ish.com.au>
> >>> Should the FreeBSD project change this minimum in the next release?
> >>> There seems to be no downside and a huge amount of pain for people
> >>> who stumble along with the defaults not knowing what a mess they are
> >>> creating to solve later.
> >>
> >> The downside is wasted space which can be significant and hence when
> >> I last suggested just this it was unfortunately rejected.
> >>
> >> We still maintain a local patch to our source tree which does just
> >> this because, as you've mentioned, we don't want the pain so its
> >> easier to just run everything as 4k.
> >
> > Another downside is 1/4th of uberblocks, 32 vs 128. Also, automatic
> > sector size detection works great for me and I've never had a need
> > to manually tweak ashift.
> >
> It works great until you start replacing older disks with new, larger 
> ones and find out that the new ones are 4k where the old ones were not.....

Is there any way (short of building a new pool) to get a reasonable idea
of how much extra space a given pool would use if converted?

Ben