RE: Oracle 11 'cold backup' while DB up.

From: <rajendra.pande_at_ubs.com>
Date: Wed, 8 Jan 2014 12:06:27 -0500
Message-ID: <7E4D006EA3F0D445B62672082A16A5650173A989_at_NSTMC703PEX.ubsamericas.net>

Good point about snapshot. How long is the snapshot duration and if the databases is essentially fully available during the snapshot

I remember there was a database with a single dedicated app that used resource manager and did a quiesce ( with I think ALTER SYSTEM QUIESCE RESTRICTED) but then you have to rely on no long running transactions and thus coordinate this with all application related processes  

So yes the "snapshot" I guess becomes extremely important  

Thanks and Regards  

• Raj Pande

UBS AG   Platform Services - Operations

  Global Service Delivery (GSDM)

  480 Washington Blvd. Jersey City, NJ 07310

  TEL# - External - +1 201 318 7597

             Internal - 19 436 7597

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Mark W. Farnham
Sent: Wednesday, January 08, 2014 11:49 AM To: howard.latham_at_gmail.com; 'ORACLE-L' Subject: RE: Oracle 11 'cold backup' while DB up.  

I guess it depends on what they mean by a snapshot, which might under the covers essentially be a broken mirror. Even for that, though, you need a period long enough in "hot backup mode" to get the full block redo to cover any Oracle level blocks that might have been fractured as writes of the underlying physical sectors at the OS level. "Long enough" can be zero time if the storage manager has a way to suspend writes and effectively tell all the dbwr to wait while the snap is made. Some volume managers for a time (maybe some still do) had a "quiesce" command that more or less paused new writes. That could work, but it seems fragile to me and onerous to prove that dbwr cannot somehow write a partial Oracle block in that model.  

If the underlying physical sector size matches the oracle block size (which is more plausible now with physical sectors of 4096 available after a long history of having essentially everything being 512), I suppose you could eliminate the possibility of fractured block writes. You'd still have a tough job proving that was correct in all possible scenarios.  

The other way is to read the database blocks through Oracle's read model, which is what RMAN does, or turn on "hot backup mode" so that sufficient to recreate changed blocks is in the redo stream. I've trusted "hot backup mode" since 6.0.37.x, and I trust Oracle to get their own read model correct for RMAN, but I don't think I trust a third party to keep up with possible changes.  

I suppose if you knew enough about the internals of ASM and this product only works with ASM there might be a way to eliminate the possibility of fractured writes. Again you'd have the problem of staying lockstep current and reproving reliability every time Oracle changed.  

Still, folks are very clever and this could be a freshly born chick. It would be interesting to hear the product name and the claimed technical specifications of how it works.  

Delphix, for example, accomplishes the goal that seems to be wanted, but I would not describe it as a cold backup. (Look to Delphix for their own description of their product.)  

mwf  

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Howard Latham
Sent: Wednesday, January 08, 2014 6:57 AM To: ORACLE-L
Subject: Oracle 11 'cold backup' while DB up.  

Ive just been told there's a tool that will do a 'cold backup' of a live database by taking a snapshot of the db at a particular time. The only way I have heard of achieving this is by having mirroring then temporarily Breaking the mirror and backing up the mirror . Any good opinions or Ideas on this would be welcome.

-- 
Howard A. Latham






Please visit our website at 
http://financialservicesinc.ubs.com/wealth/E-maildisclaimer.html 
for important disclosures and information about our e-mail 
policies. For your protection, please do not transmit orders 
or instructions by e-mail or include account numbers, Social 
Security numbers, credit card numbers, passwords, or other 
personal information.
--
http://www.freelists.org/webpage/oracle-l

Received on Wed Jan 08 2014 - 18:06:27 CET