[Info-vax] Volume shadowing and current SCSI standards ?

[abrsvc]

On Friday, April 29, 2022 at 8:12:10 AM UTC-4, Simon Clubley wrote:
> On 2022-04-28, Matthew R. Wilson <mwi... at mattwilson.org> wrote: 
> > 
> > Interesting. The wording in the Volume Shadowing Guide seem to imply 
> > that VMS itself would work with devices that don't support READ/WRITE 
> > LONG, but you shouldn't use them with Volume Shadowing. 
> > 
> 
> [snip] 
> 
> > 
> > The READ LONG and WRITE LONG commands have been removed from the latest 
> > SCSI standard. I wonder if that's why VMS refused to try to work with my 
> > target when it was reporting that it was a version SPC-5 
> > implementation... VMS may know the READ/WRITE LONG commands are no 
> > longer in the standard and so rejects the new version. (Or it may have 
> > no special knowledge of SPC-5 and later at all, and just plays it safe 
> > and refuses it because it only knows about SPC-4 and below.) 
> > 
> 
> Interesting, because that has serious implications for using VMS with 
> modern hardware, especially on x86-64, if true. 
> 
> If this statement is correct, does this mean that VMS volume shadowing 
> will no longer work with devices which use only the latest SCSI standard ? 
> 
> If so, I wonder how VSI plan to address this ? 
> 
> Simon. 
> 
> -- 
> Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP 
> Walking destinations on a map are further away than they appear.

The current HBS product requires the use of the READ/WRITE LONG commands so you are correct HBS won't work with devices that don't support it.  Many customers now use SAN devices and the "shadowing" takes place there rather than being host based which avoids the issue. I have seen the shift with many of my clients to this "new" way.  Yes HBS is valuable for many reasons, but there are alternatives that are increasingly being used today.  While this should be addressed, I don't think it has the urgency that you incidate.

Dan