I will not present RAC on this post but I would like to share with us some information on new architecture asked by customers named “RAC Extended/Stretched Cluster“.
The benefits of RAC are :
Full utilization of resources, from 1 to n nodes for one and ONLY one physical database.
Protection against Nodes failure …
But what’s happen in case of the lost of the storage ?
The first reaction is to use a second storage. But how to copy all data and which mechanism we can used to do it :
- Array based mirroring
- Host based mirroring
If we are using Array based mirroring (IBM PPRC) the solution is to use the Storage mechanism to ensure Synchronous Mirroring of active storage to passive storage but if we are loosing the active storage this failure will cause loss of full cluster, with a downtime necessary to switch the passive storage to active.
If we decide to use Host based Mirroring to ensure Synchronous Mirroring of data from one storage to an other we have the choice of several software solution (ASM, CLVM, GPFS,etc…). All writes get sent to both sets of disks and in case of one storage failure it will cause NO DOWNTIME.
But now if you have a Building Disaster ?
The solution is RAC extended/streched cluster with the implementation of RAC over 2 buildings or 2 sites.
The benefits of RAC extended Clusters is the full utilization of resources no matter where they are located.
See here several scenario of failure and consequence.
- Loosing 1 or more nodes from any sites !!!
- Loosing 1 out of the 2 storages !!!
- Loosing 1 Out of 2 sites !!!
- Loosing communication between sites !!!
The Key Point of the implementation of Oracle RAC Extended is the Architecture design. The Main key points are :
- Distance between site, quality of existing network infrastructure (CWDM, DWDM needed or Not ?)
- Disaster scenarios and Split Brain Situation to cover
- Array or Host based Mirroring
- Which Cluster files system ?
- Level of downtime supported
- Costs, etc ….
We have several presentations based on RAC Extended cluster which covered all aspects.
Here I will present only the Oracle RAC Extended Cluster : Host Based Mirroring Solution with Oracle ASM
ASM is a fantastic Oracle technology . Oracle ASM eliminates need for conventional file system and volume manager, ASM extends SAME (Stripe and Mirror Everything), Capacity on demand (Add/drop disks online, Automatic I/O load balancing, Stripes data across Disks to balance load, Best I/O throughput, Automatic mirroring and stripping), ASM is Easy to manage, ASM Can only host datafiles, not binaries.
Typical architecture with RAC / ASM
ASM to mirror Data
On Disaster, what’s next ?
Additionnal informations:
- I recommend to join RAC SIG website on http://www.oracleracsig.org/
- Send us a email to oraclibm at fr.ibm.com (email of my team Joint Solutions Center Oracle/IBM) if you have a project on RAC Extended on IBM platform. Or contact me directly