Database Reference
In-Depth Information
Basically, stretch clusters are used for a very specific reason: Building Active-Active RAC clusters, spread
over a geographically spread-out location. However, due to network latency and cost issues, Active-Active Multi-
Master Golden Gate is a much more viable option than extended distance clusters. It is important to consider that
stretch clusters are not and should not be used as a replication/Disaster Recovery technology; Data Guard is the
recommended technology for DR/failover purposes.
Extended Distance (Stretch) Clusters: Setup/Configuration Best Practices
Following are good design best practices critical to the smooth operation of extended distance clusters:
Implement/configure redundancy at the public network layer
Dense wavelength division multiplexing (Dark Fibre) is the general technology of choice for
implementing a dedicated networking tier for stretch clusters, as it provides the high-speed
low-latency network channel needed for the private cluster interconnect
Implement and configure full redundancy at the private cluster interconnect networking layer
The private cluster interconnect must be on the same subnet across all sites/nodes
The public network must be on the same subnet across all sites/nodes
Implement/configure full redundancy at the storage fabric layer
Set up/configure ASM for normal redundancy for maintaining a local copy of the database at
all sites of the RAC cluster
Implement/configure preferred mirror disk reads (ASM_PREFERRED_READ_FAILURE_
GROUPS parameter) within ASM so that the disks nearest (local) to the particular nodes are
utilized
Implement the voting disk on a 3
rd geographical site on NFS; this can be done over a WAN
Do not implement extended distance clusters over distances of more than 50-70 miles
Following are the pros/benefits/advantages of extended distance clusters:
Fast site-level failover protection solution among geographically spread-apart nodes
Active-Active configuration: full consumption/usage of all involved hardware
Scalability/High Availability RAC features not limited to a single geographical location
ASM data mirroring: multiple copies of the same data in geographically distant locations
Fast: good overall performance
By the same token, extended distance clusters are limited in their capabilities by the following
disadvantages/cons:
High costs associated with the need for high-speed networks
A dedicated redundant high-speed network is needed for the public/private network and
storage tiers. General rule of thumb: the more the geographical distance, the more the network
latency
Generally/usually, after 50-100 miles, the latency with most current technologies starts to gets
prohibitive for the smooth operation of an extended distance (stretch) cluster
No DR protection from large-scale geographical disasters due to the latency limitations
imposed by the need for a high-speed dedicated network infrastructure
 
Search WWH ::




Custom Search