Christian Bilien’s Oracle performance and tuning blog

Spotlight on Oracle replication options within a SAN (1/2)

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Some interesting issues face the many sites wishful to implement a replication for data bases between two distant sites. One of the major decisions to be taken is HOW the replication will be performed, in other words what are the options and their pro and cons? I’ll start with generalities and then present some unitary tests performed in a Solaris/ASM/VxVM/EMC DMX environment.

1. The initial consideration is synchronous vs. asynchronous replication.

Synchronous

Asynchronous

To preserve consistency, asynchronous replication must implement some sequence-stamping that ensures that write operations at the remote node occur in the correct order. Loss may thus occur with EMC SRDF/A (A stands for adaptive) or HP’s CA asynchronous, but no data corruption should be experimented.

2. Host based vs. array based replication

Data Guard and volume managers (including the ASM) can be used to mirror the data base volumes from one array to the other one.

Data Guard

Data Guard works over TCP/IP.

Pro:

Cons:

Volume management

Volume management is the only available options for some geographical clusters. RAC over Sun Cluster, RAC over ASM without 3rd party clusters, Mc ServiceGuard with the Cluster File System do not offer any other alternative (take a look at RAC geographical clusters and 3rd party clusters (HP-UX) for a discussion of RAC on geo clusters.

ASM is a also a volume manager as it is used for mirroring from one storage array to the other.

Pro:

Cons:

Array based replication

Pro:

Cons:

 

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