HP Extended Cluster for RAC Continuous availability with the flexibility of virtualization

The HP Extended Cluster for RAC architecture relies on the same components as the collocated system
configuration, but it introduces several additional key technologies. System-to-system communication is
now facilitated by the addition of a pair of Dense Wavelength Division Multiplexing (DWDM) devices
connected by dark fiber. Database replication is achieved through host-based software mirroring, and
RAC synchronizes the cache using Cache Fusion in the normal manner.
Figure 2. DWDM: Dense Wavelength Division Multiplexing
DWDM employs optoelectronic technology to simultaneously transmit multiple separate optical signals
through a single optical fiber by changing the wavelength of the incoming optical signals to permit
coexistence on a common fiber
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The transmitting DWDM device can multiplex multiple converted optical inputs over the same fiber
optic cable. The destination DWDM reverses the process; it demultiplexes the signals and converts
them back to their original wavelength. This process allows network, disk, and application
communications to share the same DWDM link and provides the capability to extend the Fibre
Channel link distances. Examples shown in Figure 2 include the multiplexing and demultiplexing of
Fibre Channel, 100Base-FX, and ESCON (Enterprise System Connection—a large-system I/O channel
architecture) transmissions.
The DWDMs and fiber optic media together provide the low latency interconnect that is essential to
RAC performance and scalability.
Dark fiber is existing fiber optic cable that has not yet been lit. This excess fiber capacity is readily
available, and using it to connect DWDM devices is rapidly gaining popularity as a cost-effective
mechanism to increase bandwidth. Because the conduit is typically dedicated to this solution, it is
always available to offer full capacity and security to the associated transmissions.
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An in-depth description of the evolution, testing, and deployment of DWDM can be found in the document titled, DWDM: A White Paper, by
Joseph Algieri and Xavier Dahan.
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