ADSM-L

Re: [ADSM-L] hypothetical situation with dedup turned on

2012-11-16 01:13:16
Subject: Re: [ADSM-L] hypothetical situation with dedup turned on
From: Alex Paschal <apaschal5 AT FRONTIER DOT COM>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Thu, 15 Nov 2012 22:09:09 -0800
Hi, David.  You can still do as you're already doing:  "audit volume
fix=yes" to find the damaged blocks, then do a "move data" against the
good data.  That would leave the unreadable data on the volume.

If the copypool volume is unavailable for a "restore volume", then the
only thing you could do is "delete volume discarddata=yes" and take the
concomitant loss of data that refers to the bad blocks. TSM should then
re-back up that data during the next full incremental backup.  (Full
incremental?  Oxymoron!  Also, maybe too much vodka. Stoli's Orange,
tonight.  ;-)

Question for the IBMers:  Is TSM smart enough to delete all of the file
objects that refer to the deduped/damaged/discarded blocks?  I would
expect so, especially with the ~new DB2 referential integrity
enforcement, but I think that's exactly what David's question is getting
at.  Could we get an authoritative answer on that?

And a more egg-head question from me:  if a few damaged blocks are
inside an aggregate, my understanding is that the entire aggregate would
be marked bad during the audit, which means TSM wouldn't be able to move
data reconstruct=yes, which would cause a larger footprint of data
loss.  Is my hypothesis correct?

Hmm.  Now that I think about it, CRC would have to be enabled on the
stgpool to detect those few bad blocks within an aggregate, otherwise
the headers/magic numbers for the aggregate/blocks would still be
readable/good and the aggregate would audit as intact. Thoughts?

Another question:  do file volumes get magic numbers?  Haha  (Sorry, I
blame the vodka.)


On 11/15/2012 12:58 PM, Tyree, David wrote:
This a hypothetical situation.

In this situation the needed tape from the copy pool is not available.
I realize that the data would be lost but how what you do next?

if we were still running v5 of TSM we would do a move data (MOVE VOL XXX) to 
save what we could then delete the volume (DEL VOL XXX). We would lose some 
data but the next backup cycle would rebackup any missing active data.

Since we are now running v6 with dedup it seems like the process would be 
different. Each volume no longer contains a complete set of files. They now 
contain parts of files.


David Tyree
Interface Analyst
South Georgia Medical Center
229.333.1155

-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of 
Grigori Solonovitch
Sent: Thursday, November 15, 2012 2:58 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: [ADSM-L] hypothetical situation with dedup turned on

Have you tried to use standard copy pol to recover any problems in primary pool?

Grigori G. Solonovitch
Senior Technical Architect  Ahli United Bank Kuwait  www.ahliunited.com.kw

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-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of 
Tyree, David
Sent: Wednesday, November 14, 2012 10:36 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: [ADSM-L] hypothetical situation with dedup turned on

                 I've had some sys admins ask me about a possible situation 
with using dedup on our primary storage pool. We are currently using dedup and 
I can't come up with a good answer.
                 Ok, our primary storage pool is using dedup. Something 
(corruption, whatever) happens to one of the files in the primary pool and the 
data needed to recover the file in the primary pool is not available.
                 I attempt to do a restore of the corrupt  file and the needed 
tape is not available.
                 How would I go about fixing that kind of a situation?
                 Back before we started using dedup we could just do a move 
volume to save what we could and then do a delete volume and the next backup of 
the server would straighten everything out. We might lose inactive copies but 
the next backup cycle would catch the missing active files.
                 With the way dedup works I'm not sure what we would do.
                 Any suggestions?

David Tyree
Interface Analyst
South Georgia Medical Center
229.333.1155


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