Re: LD devices in shadowsets on fault tolerant cluster

Ralf Gaertner wrote:
Are the disks connected to a HSZ or HSG? If so, why do you not
partition the the disks at the controller and shadow the resulting
units?

I have gotten MSCP serving working with some of the variants of vddriver
out there. However, it is more straightforward to have separate virtual
disks on each box pointing at the same container area and let the underlying
storage be served.

As long as the device name and allocation class are the same everywhere,
the devices will be synchronized. There is a vddriver variant that forces
the allocation class to a constant too.

If you want to have shdriver work with a device, though, you must be sure
the devices being shadowed implement io$_dse. (Had to add that also to
vddriver at one point when someone wanted a way to test 200-300 shadowsets
at once without having that many real disks. Initially it failed, but once
io$_dse was added, shdriver would work. Mind: I just dummied the function to
report success and to tell the requestor "yeah, boss, I deleted what you requested".
A more careful emulation might want to actually write zeroes...

It seemed odd that this worked as it did: shdriver would mysteriously fail,
even though the device driver did not report io$_dse support among legal functions.
There seem to be certain functions assumed to exist on any disk driver and never
mind what the driver says...the IRPs were being passed to vddriver regardless.

(I probably should not have been surprised: after all, there is no opportunity for extra
FDT processing...)

Vddriver has been on sigtapes and some freeware CDs; it was certainly on the
V3 one (a level down under sigtape tools).

I have no VMS V8 system to try vddriver on, but it still works fine on my V7.3+
systems and is available in source.

Some of the foregoing should be useful with lddriver if desired too.

Glenn Everhart
.

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