RE: Oracle replication with EMC2

From: Zanen, dhr. J.A. \(Jack\) van <zanenj_at_noord-holland.nl>
Date: Fri, 21 Jul 2006 15:05:04 +0200
Message-ID: <3F3DA71F9874CD4086264FE41557128546E351@pnh564.noord-holland.nl>

Correct, inomplete recoveries might be an issue. With vendor supplied utilities the database can be backed up for disaster recovery scenarios. As you stated this does a begin and end backup under the hood.

Van: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] Namens Hameed, Amir Verzonden: vrijdag 21 juli 2006 14:44
Aan: oracle-l_at_freelists.org
Onderwerp: RE: Oracle replication with EMC2

We have been using the BCV split method with Oracle hot backups for the last few years and it has been working fine. We use TimeFinder's symioctl utility to put the database in hot backup mode, which essentially issues Oracle's begin ..end commands under the hood. We are not using consistent splits where the IO is frozen via powerpath. I believe I had found an issue during testing with this approach when doing incomplete recovery.

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Zanen, dhr. J.A. (Jack) van

	Sent: Friday, July 21, 2006 2:33 AM
	To: oracle-l_at_freelists.org
	Subject: RE: Oracle replication with EMC2

	Hi

	 

	We had a lengthy discussion about this at a previous site where

the person in charge of wheeling this in refused to see our point or contact the vendor.

Our backup strategy revolved around BCV splits that we, the DBA team, did not approve of.

Above mentioned person knew better and refused to listen to all our concerns and advise. We had to get the vendor to send him some documents to point out to him that if you planned to use BCV for backup you'd have to put the tablespaces in backup mode.

BCV's are restartable images, I believe is what they call these BCV splits. (been a while)

Jack

Van: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] Namens Matthew Zito

	Verzonden: vrijdag 21 juli 2006 1:58
	Aan: rshamsud_at_jcpenney.com; adar666_at_inter.net.il
	CC: oracle-l_at_freelists.org
	Onderwerp: RE: Oracle replication with EMC2

	 

	 

	All a consistent split does, on the symmetrix, is freeze IOs to

the volumes while the split is in progress. This is because a BCV relationship is like this:

	Lun 1 - M1-M2--M3
	Lun 2 - M1-M2--M3
	Lun 3 - M1-M2--M3
	
	Where each M is a physical disk.  When you split them, its like

a zipper pulling down:

	Lun 1 - M1-M2-  -M3 (split completed)
	Lun 2 - M1-M2- -M3 (split in progress)
	Lun 3 - M1-M2--M3 (not split yet)
	
	So, if you're striping with, say, a volume manager across those

three luns, you could have a situation where you do a long write that covers all three luns, and since the split was in progress, one of the BCV disks got the write and the others didn't, resulting in inconsistent data.

The consistent split freezes the IOs, so that its impossible for a write to go to a disk that hasn't split yet. However, to the database, this still looks like a shutdown abort, or a server crash. EMC still recommends doing the begin backup before you do this.

	Thanks,
	Matt
	--
	Matthew Zito
	Chief Scientist
	GridApp Systems
	P: 646-452-4090
	mzito_at_gridapp.com
	http://www.gridapp.com
	
	
	
	-----Original Message-----
	From: oracle-l-bounce_at_freelists.org on behalf of Riyaj
Shamsudeen
	Sent: Thu 7/20/2006 2:55 PM
	To: adar666_at_inter.net.il
	Cc: oracle-l_at_freelists.org
	Subject: Re: Oracle replication with EMC2
	
	 >>When they do the bcv mirror split, they don't inform Oracle
(put
	tablespaces in hot backup mode), so it seems these files will
not be
	 >> consistent for what  Oracle expects.
	
	It is possible to have consistent backup without altering the
	tablespaces in to backup mode, using a special type of split
known as
	consistent BCV splits. This method is supported by EMC for
Oracle
	database backups and mentioned in various documents. You need
powerpath
	or ECA for the consistent split to work. I/O to that device is
frozen
	while the split is underway.
	
	Even then, I would be inclined to alter the tablespaces to
backup mode
	and then split.
	
	Thanks
	Riayj
	
	Yechiel Adar wrote:


	>> <.. snipped...>

	>>   When they do the bcv mirror split, they don't inform Oracle
(put
	>> tablespaces in hot backup mode), so it seems these files will
not be
	>> consistent for what Oracle expects.


	>> <.. snipped ..>

	>>
	> --
	> http://www.freelists.org/webpage/oracle-l
	>
	>
	>

	
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Received on Fri Jul 21 2006 - 08:05:04 CDT