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March 13th, 2012 00:00
Oracal RAC Architecture with Data Guard
Oracle RAC relies on clustered hardware and permits multiple instances to share a single database. RAC offers high availability with Transparent Application Failover (TAF) in which active sessions on a failed node or instance can be automatically failed over to surviving instances on other nodes. RAC also provides scalability. The workload can be spread among all nodes, while maintaining constant response times.
Oracle Data Guard ensures high availability, data protection, and disaster recovery for enterprise data. Data Guard provides a comprehensive set of services that create, maintain, manage, and monitor one or more standby databases to enable production Oracle databases to survive disasters and data corruptions. Data Guard maintains these standby databases as copies of the production database. Then, if the production database becomes unavailable because of a planned or an unplanned outage, Data Guard can switch any standby database to the production role, minimizing the downtime associated with the outage. Data Guard can be used with traditional backup, restoration, and cluster techniques to provide a high level of data protection and data availability.
My question is how we can use both RAC and DG together to provide high availability to both instances and primary database? If I have a multi nodes RAC with one instance on each node, how many standby databases should I have?
MR_Ora
7 Posts
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March 14th, 2012 18:00
hi,
as you have analyzed, RAC is designed for HA and scalability on production site, while data guard (DG) is designe for diaster recovery(DR), generally DG sitting in another location.
however, you can use both architecture to ensure max. business continuity. in RAC env, becuase multiple instances are shared single common DB, hence the configuration is similar to standalone DB. the tricky thing is that if RAC is using ASM disks, but if you want DG to be on normal file system, you need some work(what we have communicated with oracle support is that this architecutre is not supported by oracle, but it's working). oracle recommends using same ASM disk on DG site.
reseach
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225 Posts
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March 15th, 2012 01:00
Upon my understanding, my response to your inquires is following,
Q1, Yes
Q2, you could up to 30 standby DB in 11gR2
BartS
46 Posts
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April 2nd, 2012 01:00
Oracle has a name for this: Maximum Availability Architecture (MAA). More info here: http://www.oracle.com/technetwork/database/features/availability/maa-090890.html and a white paper: http://www.oracle.com/technetwork/database/features/availability/twp-databaseha-11gr2-1-132255.pdf
(just ignore all the marketing mumbo jumbo in the paper)
In short:
Oracle RAC - makes database highly available. Using stretched RAC this can be over some distance as well (and to make that more robust and simple, take a look at VPLEX ).
Oracle does not refer to RAC as a D/R tool. So in a full MAA architecture you have RAC (either local or stretched) for HA, plus Data Guard for D/R over longer distance (again, EMC offers storage based replication such as SRDF or Recoverpoint as a more enterprise-ready alternative for DG).
As stretching RAC requires 2 sites plus servers, adding a 3rd site with another server and infrastructure can be expensive. So customers are trying to cut corners by combining HA and DR in one (using only RAC in a stretched setup without Data Guard) but this can be tricky.
In an ideal environment where money does not matter, you would have a twin datacenter with stretched RAC on VPLEX to provide extreme HA (can even survive a complete datacenter outage without downtime) plus a longer distance site with Data Guard (or even better, EMC SRDF or RP) replication to protect from regional disasters, network issues, virus/hackers etc.
That said, if you are smart you use the standby servers for other purposes (test/dev/backup/DWH load/reporting) so your expensive standby server with even more expensive DB licences does not sit idle for years if disasters do not strike...
Regards
Bart