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Cluster Interconnect Products

Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.


Many of the Cluster vendors have designed very competitive technology. Many of the interconnect products come close to the latency levels of the SMP bus. Technologies like Memory Channel, SCI and Myrinet support virtual shared memory space by means of inter-nodal memory address space mapping. Connections between nodes are established by mapping part of the nodes virtual address space interconnect interface. Because of the memory mapped nature of the interface, transmitting or receiving overhead is similar to an access to local main memory. This mechanism is the fundamental reason for the low latency levels as seen in Memory Channel, SCI and Myrinet.

Table 3.1 summarizes the various interconnect capabilities

Measurement

SMP Bus

Memory channel

Myrinet

Sun

SCI

Gigabit Ethernet

Infiniband

Latency (?s)

0.5

3

7 to 9

10

100

< 10

CPU overhead (?s)

< 1

< 1

< 1

 

~100

 

Messages/ sec (million)

> 10

> 2

 

< 0.1

Bandwidth MB/sec

> 500

> 100

~ 250

~70

~ 50

10 to 30

Gb

Table 3.1: Various Interconnect Capabilities

Some of the popular interconnect products and technologies will be examined next.

Memory Channel - The memory channel interconnect is a high-speed network interconnect and provides applications with a cluster-wide address space. Applications map portions of this address space into their own virtual address space as 8 Kbytes pages and then read from and write into this address space just like normal memory.  This is available for Alpha-based HP (now Compaq) clusters.

Myrinet - Myrinet is a cost effective, high performance, packet communication and switching technology. It is widely used in Linux Clusters. Myrinet software supports most common hosts and operating systems. The software is supplied open source.  Myrinet implements host interfaces that execute a control program to interact directly with host processes (OS bypass) for low latency communication, and directly with network to send, receive, and buffer packets.

Scalable Coherent Interconnect - SCI is Sun's best performing cluster interconnect because of its high data rate and low latency. Applications that stress the interconnect will scale better using SCI compared to using lower performing alternatives. Sun SCI implements Remote Shared Memory (RSM), a feature that bypasses the TCP/IP communication overhead of Solaris. This improves cluster performance. The SCI is Sun's highest performing cluster interconnect for Sun Cluster hardware/software. It is available for the Sun Fire 4800 and 6800 servers.

Veritas - Database Edition/Advanced Cluster communications consists of Low Level Transport (LLT) and Group Membership Services (GAB). LLT provides kernel-to-kernel communications and functions as a high performance replacement for the IP stack. Use of LLT rather than IP reduces the latency and overhead associated with the IP stack.

HP Hyper Fabric (HMP): HP Hyper-Fabric supports standard TCP/UDP over IP and HP?s proprietary Hyper Message Protocol. Hyper Fabric extends the scalability and reliability of TCP/UDP by providing transparent load balancing of connection traffic across multiple network interface cards. HMP coupled with OS bypass capability and the hardware support for protocol offload provides low latency and extremely low CPU utilization.

Infiniband Interconnect

Infiniband is an emerging standard that will help businesses build an ideal cluster database platform. This standard specifies channels that are created by attaching Host Channel Adapters (HCA) between servers for inter-process communication.

Some of the significant features of Infiniband include:

* Infiniband allows HCA to transfer data directly into or out of application buffers.

* Data transfers are initiated directly from user mode, thus eliminating a costly context-switch to kernels. As a result, there is no system buffer involved.

* Supports up to 3.0 Gbits/Sec bandwidth. Because it allows bundling of multiple channels, effective bandwidth can grow appreciably.

* Memory Windows provides a way for the application to grant remote read/write to a specified buffer at a byte level granularity. RDMA write and read allow a clustered application, such as Oracle RAC, to transfer data blocks directly from the cache in one instance to the cache in another instance in cluster.

* Reliability built into hardware eliminates the need for implementing additional checking in the application and thus saves CPU cycles at process level.  

For building a high performance Oracle Real Application Cluster, the selection of the right interconnect is important. Care should be taken to select the highest speed, most appropriate technology that is suitable to one?s environment.

 


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.

http://www.rampant-books.com/book_2004_1_10g_grid.htm


 

 
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