Oops
----- Forwarded by Robin Sharpe/WA/USR/SHG on 12/20/01 10:01 AM -----
                    Robin Sharpe
                    Robin Sharpe

                    12/20/01 09:14 To:   michael.bartl AT de.cw DOT com
                    AM             cc:
                                   Subject:
                                         Re: Incremental forever -- any 
problems? (Scary thoughts)(Document link: Robin
                                         Sharpe)




But wait a miniute.... doesn't the multi streamed backup work by allocating
a session to each filespace (filsystem or disk partition)?  I'm not sure
you would get multiple streams if you are only backing up a single
filespace.  If that is true, then I would guess that Tivoli will implement
a multi-stream restore in the same way -- one session for each filespace
being restored.

On the other hand, I don't think there is any technical reason why the
backup couldn't split even a single directory between two sessions.  But
that's not true for restores (as you have all said already)... it will only
work if the data is on multiple tapes.  However, let's assume we have a
non-collocated pool containing a client with a wide variety of data... 30%
that rarely changes, 30% changes weekly, and 40% changes daily, and all of
the data is on a single filespace.  After several months of backups the
active backup data will probably be spread over several tapes.  We now need
to restore that filespace due to a disk crash.  A well-implemented
multi-stream restore should be able to sort the data by tape volume and
start a session for each volume.  Note that we can't even do that manually
now, because we have no way of knowing what tape contains what active
versions.

I think it's important for Tivoli to implement multi streaming in this way
since so many NT clients have only one or two filespaces... In our shop,
most have two -- a C: drive for NT and a D: drive for files or Notes or
whatever.

Robin Sharpe
Berlex Labs




                    Michael Bartl
                    <michael.bart
                    l AT CW DOT COM>     To:    ADSM-L AT VM.MARIST DOT EDU
                                  cc:    (bcc: Robin Sharpe/WA/USR/SHG)
                    12/20/01      Subject:
                    03:51 AM             Re: Incremental forever -- any 
problems? (Scary thoughts)
                    Please
                    respond to
                    michael.bartl







Hi Kelly,
your're right, a multistream restore is one of the items on top of our
wishlist.

Just one thought on collocation:
With collocation you can't mount as many tapes as without, ok. But with
collocation, data from one node is much more compactly written to one
tape. So when you don't use collocation and you have to mount 50 instead
of 7 tapes (or even 7 instead of one) you have to keep in mind that TSM
has to skip 6/7 of the data on the tapes while reading them.

So collocation would remain an important feature, the benefit just
decreasing in size (compared to now).

Best regards,
Michael


Kelly Lipp wrote:
>
> On the wishlist item:
>
> I have heard talk about implementing an automatic multi-stream restore
> similar to what we have now with backup and resourceutilization.  This
will
> be slick but then only really slick if one uses collocate=filespace.  I
> believe it will still provide better restore times since it will know
what
> tape volumes client data is on and will mount multiple volumes.  If one
> thinks about this for a few minutes, one realizes the whole thing is damn
> complicated.  Also, it would appear that collocation would not be a good
> thing if you use this technique: you want data on multiple tapes.
>
--
Michael Bartl                               mailto:michael.bartl AT cw DOT com
Michael Bartl                               mailto:michael.bartl AT cw DOT com
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