[Info-vax] HBMM vs HBVS

[Robert A. Brooks]

On 10/24/2011 4:44 PM, Phillip Helbig---undress to reply wrote:
> With SHOW SHADOW and SHOW DEVICE/BITMAP, one can see the HBMM bitmaps,
> information related to them etc.  Since someone here mentioned that HBVS
> and HBMM, though similar in functionality, don't have much overlap, and
> that common bitmaps came only sometime after 7.3-2, I'm wondering where
> similar information about HBVS is stored.

Huh?  HBVS = Host-Based Volume Shadowing
       HBMM = Host-Based Minimerge (or MiniMerge or Mini Merge, etc...)

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.

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.

Prior to HBMM, the WBM technology used up to 6 bitmaps per virtual unit.
With HBMM, another 6 additional slots were added.  At that time, slots
1-6 were for minicopy and 7-12 were for HBMM.  I'm not sure how the
introduction of convertible bitmaps affected that strategy.

> Another question: Is there any reason to use anything other than "*" for
> master list if there are not more than 6 nodes in the cluster?

Sure.  There may be a reason why you don't want a specific node or nodes
to have master bitmaps.  If you cannot think of a reason, then yeah,
using the wildcard character makes sense.

For more bitmap fun and games, try SDA> SHOW DEVICE /BITMAP

                         -- Rob