GEOM mentor request

[symbolics at gmx.com]

On Fri, Nov 01, 2013 at 01:23:12PM -0600, Warren Block wrote:
> On Fri, 1 Nov 2013, symbolics at gmx.com wrote:
> 
> >  + Implement new things. Some ideas I have had:
> >    + GEOM "ERASE" - Rewrite deletes into random writes.
> >    + GEOM "PLUG" - Persistent version of the connect/disconnect verbs
> >      where the flag sits in the class metadata. This might be a cleaner
> >      approach, rather than adding the verbs to all the existing
> >      providers.
> >    + GEOM "TAP" - Allow userspace processes to hook into the GEOM
> >      API. Intended for debugging and development.
> >    + GEOM "WCACHE" - Allow you to use small, fast provider as a buffer
> >      for a larger, slower provider.
> >    + GEOM DTrace provider. Provide GEOM specific probes to complement
> >      the IO provider.
> >  + Probably other bits I can't remember right now.
> 
> How about an explicit geom retaste command?  "true > /dev/ada0" is
> misleading to the reader.

Yes, that would be good. It's on my list.

> Also, a RAM-cached version of gmirror that would report writes finished 
> as soon as the faster drive finishes.  Kind of the opposite of the 
> WCACHE above.  This would permit creating mirrors of an SSD and hard 
> drive without performance loss, at least up until available write 
> buffer space runs out.  This one may not be so easy.

I can see the benefit. This would be like a mirror with a journal. As
long as it has a different name from mirror, 'lazy mirror' ?, I think it
would be interesting. The only concern I have would be that some users
could use it and assume the normal mirror semantics, e.g. that all discs
are equally redundant, which wouldn't be true.

--sym