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

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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 ..>

>>

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