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Cloning a large RAC database

Oracle Tips by Steve Karam

See related notes: Fast cloning of Oracle databases

Question:  We have a specific need to clone a RAC database that is in archivelog mode and is up and running and is about 2 terabytes. We?ve been able to clone the smaller databases in archivelog mode with little impact on the database being cloned and would like to use this option for the multi terabyte RAC clusters database. How do you clone a large multi terabyte RAC database?

Answer:  Oracle's Grid Control uses the RMAN DUPLICATE feature in order to do its RAC cloning.  This RMAN feature uses a database backup as the basis for the cloning procedure.  The backup is transferred and restored on another server and put into action.

Unfortunately, the only real way to customize a large RAC clone with RMAN this is to allocate more channels.  You can run the DUPLICATE command on your own in RMAN, without using RAC Grid Control.  When you do so, just specify multiple AUXILIARY channels of device type DISK.  The more you specify, the faster your duplicate will take place.  You can find a better description of RMAN terminology (including how channels work) here.

You may be able to allocate more AUXILIARY channels in RAC Grid Control as well, but I'm somewhat sure you cannot.  I don't have a Grid Control server to look at at the moment, but if you see options to allocate more channels when cloning that's what you want in order to speed up the cloning process.

With a multi terabyte RAC cluster database, you may want to consider a combination of RMAN or Transportable Tablespaces and some sort of hardware cloning/snapshot if possible.  If you are using NetApp or EMC for data storage, there may be snapshot capabilities you can take advantage of in order to clone the datafiles quickly.

If you have no option to use a snapshot technology, another approach to RAC cloning is to mount the target system's drives locally on the primary system.  This way you can use RMAN to backup the datafiles as datafile copies straight to the target disk instead of having the files go over the network (like the DUPLICATE command does).  Once you're done with the RAC database clone, dismount the target's disks from the primary and mount them to the target server.

Transportable Tablespaces are also well liked for large databases, but they cause tablespaces to be in READ ONLY mode while copying...meaning you will not have 100% uptime on the target.
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