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Oracle Omotion tips

Oracle Database Tips by Donald BurlesonSeptember 6,  2015

The Oracle Omotion instance migration utility

Omotion is an online migration utility (new in 11gR2) that is used with RAC One Node to facilitate super fast instance relocation is cases of server failure.  This is part of Oracle Corporations' acknowledgement of the server consolidation movement and the 2nd age of mainframe computing.

While details from Oracle are sketchy, it's a safe bet that Omotion performs instance relocation is  a fashion similar to it's predecessors, Savantis Systems with their DB-Switch invention, an offshoot of the Database Area Network (DAN) approach.

Savantis Systems uses a high-speed database switch (dbSwitchâ„¢) which is placed between the application layer and the database layer. This switch enables Oracle databases to be transparently relocated onto new servers without the need to modify applications connections to the database.

In a similar fashion, Oracle Omotion might use a SAN, whereby a new server (preloaded with an instance init.ora file), should acquire the database files from the SAN, mount them to the new server, and quickly re-start the RAC instance:

The Database Area Network (DAN) architecture.

See here for details on how Oracle instance relocation works using DAN and SAN technology.  In the olden days, we did instance relocation with a SAN environment, using the following steps:

1. The Oracle instance or the server crashes.

2. A dead connection probe (DCD) detects the outage and we un-mount the SAN data file systems from the source server (if it's awake).

3. We then mount the database files onto the failover server using SAN.

4. We re-start the instance on the new server, using a pre-loaded init.ora file.

5 We use a failover routing mechanism like transparent application failover (TAF) to redirect transactions accessing the database (VIP) to the new server.

A typical time for an Oracle instance relocation is less than 20 seconds, not true continuous availability, but certainly better than a catastrophic unplanned outage.

Oracle Instance relocation make sense!

An instance relocation scheme makes sense because it uses far less resources than Data Guard (which requires a standby server) and Streams failover.  With instance relocation, a single standby server might serve for hundreds of instances.

Dynamic instance relocation can make Oracle databases behave like "black boxes." This means that the OS architecture is not important because the database is independent of the OS. For example, Oracle Omotion likely allows relocation to any OS with the same Endian format, including AIX, Linux, Solaris, or HP/UX.

As this Omotion technology matures, it's likely that predictive analytics might be used to predict when the database will experience stress and relocate it to a larger server, just in time to accommodate the increased processing need.



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