Discussion:
MDISK versus LINK
(too old to reply)
Don
2006-01-31 17:51:05 UTC
Permalink
I have a situation where multiple z/OS guests need to share DASD. In the
past I have used a userid as a disk holder with MDISKs using DEVNO and MWV.
The guests would then LINK to the MDISKs using MW. It has been suggested
that I eliminate the disk holder userid and use MDISK statements only. Each
guest would then have an MDISK for the same address. For example,
MDISK D000 3390 DEVNO D000 MWV

Does anyone know if there is any advantage or disadvantage to one way over
the other?
David Boyes
2006-01-31 18:24:30 UTC
Permalink
Post by Don
I have a situation where multiple z/OS guests need to share
DASD. In the past I have used a userid as a disk holder with
MDISKs using DEVNO and MWV.
The guests would then LINK to the MDISKs using MW. It has
been suggested that I eliminate the disk holder userid and
use MDISK statements only. Each guest would then have an
MDISK for the same address. For example, MDISK D000 3390
DEVNO D000 MWV
Does anyone know if there is any advantage or disadvantage to
one way over the other?
Both work, but the disadvantage of the multiple MDISK definition method
is that you have to keep multiple entries in multiple places absolutely
in sync 100% of the time. If one is off-by-one or you forget to update
one, Bad Things Ensue, and z/OS will get mucho cranky.

The MDISKs will also show up as overlaps in your directory management
tooling, which is OK if you understand why, but ignoring error messages
is a bad habit, and you might miss an important one later if you get
accustomed to ignoring errors on mapping.

You've got the best (IMHO) method in place now. Don't change it. You
don't need the hassle, nor does the next person to come along.

-- db
Stephen Frazier
2006-01-31 18:36:29 UTC
Permalink
If you want to use reserve/release on the disk you must have all systems link to
the same MDISK with MWV on the statement. That is the way you have it now. If
you change it to have a different MDISK statement for each guest then
reserve/release will not work. I don't know if z/OS uses reserve/release to
serialize access to dasd or if it uses something else.

You are doing it right now. If you make the change I can not guarantee that it
will fail. :)
Post by Don
I have a situation where multiple z/OS guests need to share DASD. In the
past I have used a userid as a disk holder with MDISKs using DEVNO and MWV.
The guests would then LINK to the MDISKs using MW. It has been suggested
that I eliminate the disk holder userid and use MDISK statements only. Each
guest would then have an MDISK for the same address. For example,
MDISK D000 3390 DEVNO D000 MWV
Does anyone know if there is any advantage or disadvantage to one way over
the other?
--
Stephen Frazier
Information Technology Unit
Oklahoma Department of Corrections
3400 Martin Luther King
Oklahoma City, Ok, 73111-4298
Tel.: (405) 425-2549
Fax: (405) 425-2554
Pager: (405) 690-1828
email: stevef%doc.state.ok.us
william JANULIN
2006-01-31 18:46:52 UTC
Permalink
I agree with Dave.....if it ain't broke, don't fix it.
Also,
if you change volumes down the road, you only have
only place to make the change, not the multiple
MDISKS.
Post by Don
Post by Don
I have a situation where multiple z/OS guests need
to share
Post by Don
DASD. In the past I have used a userid as a disk
holder with
Post by Don
MDISKs using DEVNO and MWV.
The guests would then LINK to the MDISKs using MW.
It has
Post by Don
been suggested that I eliminate the disk holder
userid and
Post by Don
use MDISK statements only. Each guest would then
have an
Post by Don
MDISK for the same address. For example, MDISK
D000 3390
Post by Don
DEVNO D000 MWV
Does anyone know if there is any advantage or
disadvantage to
Post by Don
one way over the other?
Both work, but the disadvantage of the multiple
MDISK definition method
is that you have to keep multiple entries in
multiple places absolutely
in sync 100% of the time. If one is off-by-one or
you forget to update
one, Bad Things Ensue, and z/OS will get mucho
cranky.
The MDISKs will also show up as overlaps in your
directory management
tooling, which is OK if you understand why, but
ignoring error messages
is a bad habit, and you might miss an important one
later if you get
accustomed to ignoring errors on mapping.
You've got the best (IMHO) method in place now.
Don't change it. You
don't need the hassle, nor does the next person to
come along.
-- db
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
Nix, Robert P.
2006-01-31 19:15:17 UTC
Permalink
I would be very interested in who, and with what background, suggested the multiple MDISK approach, as it flies in the face of everything we've been taught by Mom over the years, all the way back to VM/370. (Maybe back to CP-67.)


--
Robert P. Nix Mayo Foundation
RO-OC-1-13 200 First Street SW
507-284-0844 Rochester, MN 55905
-----
"In theory, theory and practice are the same, but
in practice, theory and practice are different."

-----Original Message-----
From: VM/ESA and z/VM Discussions [mailto:VMESA-***@LISTSERV.UARK.EDU] On Behalf Of Don
Sent: Tuesday, January 31, 2006 11:51 AM
To: VMESA-***@LISTSERV.UARK.EDU
Subject: MDISK versus LINK

I have a situation where multiple z/OS guests need to share DASD. In the
past I have used a userid as a disk holder with MDISKs using DEVNO and MWV.
The guests would then LINK to the MDISKs using MW. It has been suggested
that I eliminate the disk holder userid and use MDISK statements only. Each
guest would then have an MDISK for the same address. For example,
MDISK D000 3390 DEVNO D000 MWV

Does anyone know if there is any advantage or disadvantage to one way over
the other?
Steve Gentry
2006-01-31 19:28:00 UTC
Permalink
I don't know about the reserve/release part, but when I was a VSE
sys.prog. I also had one userid owning the mdisks
and all users linked to that mdisk-owning-user.
Steve G.





Bill Stephens <***@sungard.com>
Sent by: VM/ESA and z/VM Discussions <VMESA-***@LISTSERV.UARK.EDU>
01/31/2006 02:23 PM
Please respond to VM/ESA and z/VM Discussions


To: VMESA-***@LISTSERV.UARK.EDU
cc:
Subject: Re: MDISK versus LINK


FWIW, we've always built the directories for our customers who recover
under VM with a DASD userid owning all the MDISKs, and all other guests
LINK to DASD. When you're recovering MVS (don't know about VSE) you have
to do it this way if you want virtual reserve/release to work (as Steve
Frazier pointed out).

What are the advantages, aside from possible job security, of defining all
MDISKs for every instance of a pack? Sounds like a pointy-haired-boss
decision to me ...

Regards,
Bill Stephens
Sr. Technology Analyst, High Availability
SunGard Availability Services
10th floor
401 North Broad Street
Philadelphia, PA 19108
Phone: (215) 351-1099
Fax: (215) 451-2045
***@sungard.com
___________________________________________
Keeping People and Information Connected (TM)
http://www.availability.sungard.com
Schuh, Richard
2006-01-31 19:24:47 UTC
Permalink
This is a point that David missed. As Stephen says, you lose virtual RESERVE/RELEASE, something that could be disastrous if you have guests that depend on R/R, such as MVS or its progeny, sharing the disks. True, there are program products that allow MVS to share DASD without use of R/R, but you are safer assuming that these packages are either not installed or are not turned on. Nothing is lost if virtual R/R is available; nothing gained, if not.

Regards,
Richard Schuh

-----Original Message-----
From: VM/ESA and z/VM Discussions [mailto:VMESA-***@LISTSERV.UARK.EDU] On Behalf Of Stephen Frazier
Sent: Tuesday, January 31, 2006 10:36 AM
To: VMESA-***@LISTSERV.UARK.EDU
Subject: Re: MDISK versus LINK

If you want to use reserve/release on the disk you must have all systems link to
the same MDISK with MWV on the statement. That is the way you have it now. If
you change it to have a different MDISK statement for each guest then
reserve/release will not work. I don't know if z/OS uses reserve/release to
serialize access to dasd or if it uses something else.

You are doing it right now. If you make the change I can not guarantee that it
will fail. :)
Post by Don
I have a situation where multiple z/OS guests need to share DASD. In the
past I have used a userid as a disk holder with MDISKs using DEVNO and MWV.
The guests would then LINK to the MDISKs using MW. It has been suggested
that I eliminate the disk holder userid and use MDISK statements only. Each
guest would then have an MDISK for the same address. For example,
MDISK D000 3390 DEVNO D000 MWV
Does anyone know if there is any advantage or disadvantage to one way over
the other?
--
Stephen Frazier
Information Technology Unit
Oklahoma Department of Corrections
3400 Martin Luther King
Oklahoma City, Ok, 73111-4298
Tel.: (405) 425-2549
Fax: (405) 425-2554
Pager: (405) 690-1828
email: stevef%doc.state.ok.us
Loading...