IBM 990 3.4.5 Coupling Facility links

Chapter 3. I/O system structure 103

Draft Document for Review April 7, 2004 6:15 pm 6947ch03.fm

This function does not apply to IPv6 packets. TCP/IP will continue to perform all checksum

processing for IPv6 packets. This function also does not apply to ICMP checksum processing.

TCP/IP will continue to perform processing for ICMP checksum.

Checksum offload is supported by the OSA-Express GbE features (FC 1364, FC 1365) and

the 1000BASE-T Ethernet feature (FC 1366) when operating at 1000 Mbps (1 Gbps). This is

applicable to the QDIO mode only (channel type OSD).

z/OS support for Checksum offload is planned to be available in z/OS V1.5.

For Linux for zSeries support, refer to the following Web site for further information:

http://www.ibm.com/developerworks.

The z990 servers, Linux for zSeries, and z/VM work together to provide performance

improvements by exploiting extensions to the Queued Direct Input/Output (QDIO)

architecture. Adapter Interruptions, first added to z/Architecture with HiperSockets, provide an

efficient, high-performance technique for I/O interruptions to reduce path lengths and

overhead in both the host operating system and the adapter - OSA-Express when using the

OSD CHPID type.

In extending the use of adapter interruptions to OSD (QDIO) channels, the programming

overhead to process a traditional I/O interruption is reduced. This benefits OSA-Express

TCP/IP support in both Linux for zSeries and z/VM.

Adapter interruptions apply to all of the OSA-Express features available on z990, whether

offered as a new build or on an upgrade from z900 when in QDIO mode (CHPID type OSD).

The HiperSockets function, also known as internal Queued Direct Input/Output (iQDIO) or

internal QDIO, is an integrated function of the z990 server which provides users with

attachment to up to sixteen high-speed “virtual” Local Area Networks (LANs) with minimal

system and network overhead.

HiperSockets eliminates the need to utilize I/O subsystem operations and the need to

traverse an external network connection to communicate between logical partitions in the

same z990 server. HiperSockets offers significant value in server consolidation connecting

many virtual servers, and can be used instead of certain XCF link configurations in a Parallel

Sysplex.

HiperSockets are customizable to accommodate varying traffic sizes. Since HiperSockets

does not use an external network, it can free up system and network resources, eliminating

attachment costs while improving availability and performance.

3.4.5 Coupling Facility links

Following are Coupling Facility links connectivity options in the Parallel Sysplex environment.

For more information about Parallel Sysplex connectivity, see “Coupling Facility link

connectivity” on page 162.

z990 supports the following coupling link features:

򐂰Inter-System Channel-3, ISC-3 (Peer and Compatibility modes), feature codes 0217,

0218, and 0219