DFPdss DUMP provides a option (DUMPCONDITIONING ?) which allows you to
take a full-volume flashcopy of a DASD volser on IBM DASD Subsystems,
but preserve the original target volser so both volumes can be online to
allow a follow-up slower destaging of the target volume copy to tape
with dss of the on-line target volume. As long as the volume has a VTOC
Index or a VVDS, dss is able to do this in a way that allows a restore
the full volume dump of the copy with the funny volser to end up with
the correct original volser. This enables you to make snap copies of
all significant system volumes in a few seconds to a second set of
unique volsers, which with other suitable precautions can give
acceptable consistency across all volume backups, while allowing
destaging to tape (or remote DASD) to cover a much longer period without
compromising backup consistency. This can provide a simple stategy for
generating point-in-time system backups for total system recovery to a
point-in-time.
You are somewhat restricted in what you can do with individual data sets
on the FlashCopy target volume with the different volser, but this seems
a saner solution than a product that allows you to access and dump an
"off-line" DASD volume. If a volume is "off-line" that should mean
it's inaccessible to MVS, and that taking the related hardware off line
would be non-disruptive to MVS and safe to do -- obviously not the case
if you could somehow be dumping the "off-line" volume.
I can't recall the rules, but I believe IBM DASD Subsystems also
interface with z/OS to provide ways to group a collection of volumes
together in a "consistency group" for FlashCopy of multiple volsers in a
way that suppresses updates to the volumes until all in the group are
flashed.
JC Ewing
On 01/09/2013 08:24 AM, Darth Keller wrote:
Some simple answers as requested -
Each hardware vendor supplies it's own software providing the 'snapshot'
functionality. Changing hardware may necessitate changing jobs or
parameters to accommodate the different hardware functionality provided.
There are basically 2 levels - Full Volume & Dataset Level. In my
experience, the full volume functionality is generally part of the deal
when you buy the hardware. If it wasn't, you need to bargain harder.
Dataset level may or may not have an extra cost - again depends on your
deal.
Full Volume level provides an identical copy of the volume - volser,
datasets, everything. Because it's an identical volume, you can't bring
it on line to the same LPAR, but you can bring it online to another LPAR
if the original volume is not already online there. There are products
which allow you to back the copy up while it is offline. These issues
limit dataset accessibility and carry some risk if you need to understand
if you use the volume on another system. There are also issues with
multi-volume datasets. For the purposes of your discussion, I don't
think you're interested in Full Volume.
Now Dataset Level Flashcopy is more interesting because you can flash
datatsets (even multi-volume ds's) to a new name. The new dataset is
nearly instantaneously available while the actual physical copy happens in
the background. This new dataset is available to other programs &
utilities.
There are also issues to consider when there are multiple subsystems
involved. Luckily I don't have to deal with them except at DR as we can
fit into a single subsystem.
HTH's
dd keller
Please bear with me, but this is an area where my knowledge is very
limited.
I'd need a quick and simple answer for a discussion here. Don't go too
much into
various possibilities. I just need to get the big picture for now.
Snapshot functionality is offered by DASD subsystems, not by z/OS,
right?
What granularity can one get with snapshorts?
- On the sub-volume level, i.e. on the individual MVS data set level ?
- On a multi-volume level within one storage subsystem?
- On a multi-volume level within multiple storage subsystems?
-How can an application access the data in a snapshot, i.e. to create a
point in time backup?
-Is it reasonable to program, say in Java or PL/1, to backup data with
the help of snapshot technology?
- Does this require authorized functions?
--
Peter Hunkeler
--
Joel C. Ewing, Bentonville, AR [email protected]
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