By timread on Feb 25, 2009
With the announcement of Solaris Cluster 3.2 01/09 comes a new version of Sun Cluster Geographic Edition (SCGE). Among the features delivered in this release is support for replication of Oracle RAC databases using Oracle Data Guard. So it seems like a good opportunity to summarise the ways you can protect your Oracle infrastructure against disaster using the replication support provided by Sun Cluster Geographic Edition.
I'll start by breaking the discussion into two halves: first deployments using a highly available (HA) Oracle implementations, the second using Oracle Real Application Clusters (RAC). Additionally, I'll reiterate the replication technologies that SCGE supports, namely: EMC Symmetrix Remote Data Facility (SRDF), Hitachi TrueCopy, Sun StorageTek Availability Suite (AVS) and last, but not least, Oracle Data Guard (ODG). One final point to make is that SCGE support for SRDF/A is limited to takeover operations only.
HA Oracle Deployments
HA-Oracle deployments are found in environments where the cost/benefit analysis determines that you are prepared to trade off the longer outages involved in switching or failing over an Oracle database compared with the near-continuous service that Oracle RAC can offer, against the additional licensing costs involved.
Deployments of HA-Oracle can be on a file system: UFS or VxFS (stay posted for ZFS support) or on raw disk with, or without, a volume manager: Solaris Volume Manager (SVM) or Veritas Volume Manager (VxVM). Why not Oracle Automatic Storage Management you might ask? Well, while ASM is indeed supported on Oracle RAC, it poses problems when employed in a failover environment. There is a need to fail over either the ASM instance or just the disk groups used to support the dependent databases. These requirements currently preclude ASM from being supportable. Are we working on this? Of course we are!
So this gives us a set of storage deployment options that must be married with the replication options that SCGE supports and any restrictions that may come into play when deploying HA-Oracle in a Solaris Container (a.k.a zone).
Coverage is extensive: Oracle 9i, 10g and 11g are supported on file systems (UFS or VxFS) or raw devices, with or without containers and with or without VxVM, using either AVS, SRDF or TrueCopy. In contrast, SVM restricts the replication technology support to AVS only.
Why isn't Oracle Data Guard supported here, especially given that it's one of the new replication modules in SCGE 3.2 01/09? The answer lies in the use Oracle Data Guard broker as an interface to control the replication. Unfortunately, ODG broker stores a physical host name in its configuration files and after a fail-over it doesn't match that of the new host, thus invalidating the configuration. Consequently, Oracle does not support ODG broker on 'cold failover' database implementations even if this host name change could be avoided, say by putting the database into a Solaris Container.
Oracle RAC Deployments
With HA-Oracle options covered I'll now turn to Oracle RAC. As you will no doubt know from reading "Solaris Cluster 3.2 Software: Making Oracle Database 10G R2 and 11G RAC Even More Unbreakable", Solaris Cluster brings a number of additional benefits to Oracle RAC deployments including support for shared QFS as a means of storing the Oracle data files. So now you'll need to know what deployment options exist when you include SCGE in your architecture.
As we're still working on adding Solaris Container Cluster support to SCGE there is currently no support for Oracle RAC, or indeed any other data service, using this virtualisation technique.
Furthermore, I should remind you that AVS is not an option for any Oracle RAC deployment simply because it cannot intercept the writes coming from more than one node simultaneously.
On the positive side, storage replication products such as SRDF and TrueCopy are an option as they intercept writes at a storage array level rather than at the kernel level. These replication technologies are restricted to configurations using raw disk on hardware RAID or raw VxVM/CVM volumes. These storage options can then be used with Oracle 9i, 10g or 11g RAC. For a write up of just such a configuration, please read EMC's white paper on our joint demonstration at Oracle Open World 2008.
Combinations wishing to use shared QFS or ASM are currently precluded because of the additional steps that must be interposed prior to an SCGE switchover or takeover being effected. Are we looking to address this? Absolutely!
If you want unfettered choice of storage options on Solaris Cluster when replicating Oracle 10g and 11g RAC data, then the new Oracle Data Guard module for SCGE is the answer. You have freedom to choose any combination of raw disk, ASM, shared QFS deployment combination that makes sense to you. You can configure a physical standby partner in either single instance to single instance or dual instance to single instance combinations, i.e. primary site to standby site configurations. All ODG replication modes are supported: maximum performance, maximum availability and maximum protection. Although the SCGE can control logical standby configurations Sun have not yet announced formal support for use of this feature.
You've Read The Blog, Now See The Movie....
I hope that gives you a clear picture of how you can use a combination of Solaris Cluster and the various replication technologies that Sun Cluster Geographic Edition supports to create disaster recovery solutions for your Oracle databases. If you would like to see demonstrations of some of these capabilities, please watch the video of an ODG setup and an SRDF configuration on Sun Learning Exchange.Tim Read
Solaris Cluster Engineering