[Info-vax] HBMM vs HBVS

[Kenneth Fairfield]

On Tuesday, October 25, 2011 12:41:32 PM UTC-7, Phillip Helbig---undress to reply wrote:
> In article <j86ekf$ev4$1... at usenet01.boi.hp.com>, "Robert A. Brooks"
> <r... at aitchpee.com> writes: 
[...]

> > I have no idea what you mean by
> >        "Since someone here mentioned that HBVS and HBMM, though
> >         similar in functionality, don't have much overlap..."
> > 
> > HBMM is subordinate to HBVS; HBVS can function without HBMM, whereas it
> > makes no sense to talk about HBMM without HBVS.
> 
> OK.  Maybe I should have written "minicopy vs minimerge".

Yep.  That's a very different question.

> 
> > HBMM uses the Write Bitmap technology that first appeared in V7.3 (and 
> > backported to V7.2-2). It was created to enable HBVS minicopy.
> 
> OK.

And for a little history, folks I worked with at
Intel (and I'm sure there were other customers as
well) were very unhappy to find that shadow sets on
FC-attached disks (Brocade SAN and HSGs) would undergo
a FULL MERGE whenever there was a "bump" in the 
cluster (yes, usually a node crash).  They/we
really missed minimerge as implemented on CI (HSJs
and HSCs).  Intel brought a lot of pressure on
Compaq to fix this omission.

My recollection, now quite cloudy, of the initial
design was to have special HSG firmware work with 
a reserved area on each shadow member which would
function as the write bitmap.  That work went on 
and on and on over about a three year period (at 
least).

At some point, whether during a review or at some
implementation check-point, storage engineering
determined the design just wouldn't fly and they
dumped.  

However, by that time minicopy was in production 
and they realized they could leverage the minicopy
bitmaps for minimerge.  It didn't take long after
that to get minimerge out the door.  We were on 
v7.3-1 at the time, but some small glitches, similar
to things you found in the command syntax/parsing,
weren't fixed until the v7.3-2 ECO came out.

   -Ken