Multinode Persistent Sessions: The Sysplex Data Sharing

End Game

Bryant L. OsbornBank of America

Introduction• APPN- (Advanced Peer-to-Peer Networking) VTAM facility introduced in the late 1980’s.

• HPR - (High Performance Routing) extension to reroute sessions around links that have failed.

What does this have to do with the future of data sharing? Everything.

Definitions• Scalability - a measure of the practical limits to how large a system can be.

• CEC - Central Electronics Complex, or mainframe, box, footprint, etc.

• CPC - Central Processor Complex, or a CMOS CEC.

• CS/390 - New name for VTAM

Sysplex Benefits

•Improved scalability•Continuous availability

(Besides software discounts)

Improved Scalability

Irwin F. Kraus, “The Parallel Sysplex as SMP: Viewing Performance, Capacity, and Scalability through a Familiar Lens”, CMG96 Proceedings, December, 1996

Improved Scalability

•For MVS, maintaining the “general case” has too much overhead to go much above 12 processors.

•Sysplex no longer supports the “general case”.

•Sysplex builds systems by adding MVS images to a Sysplex

Improved Scalability“When a user architects a parallel sysplex, the user decides how much data is to be shared, usually much less than 100%. The user decides how many processing nodes will be used and what capacity and performance. The user-system-architect has a lot of control over minimizing overhead and maximizing scalability in a ‘parallel sysplex computer’ ”

- Irwin Kraus

Improved Scalability•MVS goes ‘massively parallel.’ Parallel Sysplex increases MVS scalability to make truly gigantic workloads possible.

•But wait! Hardware improvements have resulted in CECs with 1000+ MIPS

•Which way to go?

Continuous Availability

•As workloads get larger and larger, the risk from an outage becomes greater and greater

•Parallel Sysplex may allow continuous availability for overnight batch workloads, but what about interactive workloads with logged-on users?

Continuous Availability

The $64,000,000 question: What good is it to have a single gigantic workload if the organization cannot afford even a brief outage of the entire system?

Is anyone really willing to put all their proverbial eggs in one basket, and run the risk that a single outage could take down the entire workload?

Single-Node Persistent Sessions

• A VTAM facility• There are two kinds of persistent sessions. The

kind that exists today is called ‘single-node persistent sessions.’

• VTAM keeps session state information about VTAM users. When a subsystem crashes, VTAM can maintain the sessions for a specified period of time.

Single-Node Persistent Sessions

The Benefits of SNPS

• Saves users from having to re-establish VTAM sessions (VTAM keeps ACBs open)

• Saves application time to clean up failed sessions, but

• Users can do no work until the application is brought back up, and

• What happens if VTAM itself fails??

What if . . .

Wouldn’t it be nice is there was a way that users could be reconnected to another MYCICS on CEC-B by reconnecting them through a VTAM-B? What a great idea! But is it possible? What you call it?

Multinode Persistent Sessions• Users of a failed application are

reconnected through a different VTAM to another application on another LPAR. How is this possible?

• Uses APPN’s High Performance Routing (HPR) facility

• Allows fast recovery from failures of all kinds

Multinode Persistent Sessions• SNPS stored user session information in

dataspace. Where is the only place this information could be stored in a Sysplex where:

a) all VTAMs can get to it, andb) information will not get trashed by any

failure?• Requires a coupling facility and more that one

LPAR

Multinode Persistent Sessions• CICS implementation - MVS Automatic

Restart Manager will start another region on another LPAR. VTAM will use HPR to perform a path switch to move the connection endpoint

• IMS implementation - will probably allow reconnection to an existing IMS. Have users open multiple ACBs at logon time, and switch between them???

VTAM Primer• Node - is the endpoint of a

communication link• Subarea Networks - hierarchical

networks• APPN Networks - Peer-oriented

networks

Essential Subarea Networks• Key word is ‘hierarchy’• VTAM is ‘king’ of the hierarchy. Also

called a System Services Control Point (SSCP).

• Network Control Program (NCP) in a communications controller is second

• Everything else is a peripheral node that comes in third

Essential Subarea Networks• LU (logical unit) - is a port where users

connect to the node. Every LU is owned by a VTAM (SSCP). LUs request request network services from VTAM (SSCPs).

• PU (physical unit) - manage links and routing. (Similar to APPN ‘control points.’)

Subarea Network Nodes

• Type 5 Node - VTAM (SSCP)• Type 4 Node - NCP in a communications controller.

Requires a type 5 node to provide all network services• Type 2 Node - Peripheral node that cannot perform

routing. They are dependent on the VTAM (SSCP).• Type 2.1 Node - Peripheral node with limited peer-to-

peer capabilities. Can be independent of the VTAM (SSCP) if using LU 6.2 communication.

Subarea Network Nodes

Subarea Networks• All paths must be manually defined. Route selection

is chosen from from predefined routes.• Virtual Routes (VRs) - logical paths on which

sessions are carried. SSCP (type 5) and NCP (type 4) nodes establish and maintain VRs.

• Class of Service (COS) - sessions are assigned to VRs on the basis of an assigned class of service.

• Management and Control Sessions - SSCP-SSCP, SSCP-PU, and SSCP-LU

Essential APPN Networks• Key word is ‘peer’ which means ‘of equal

standing’• Network Nodes (NNs) - provide all

network services• End Nodes (ENs) - provide LU ports and

rely on Network Nodes (NNs) for the rest.

Essential APPN Networks

• Control Point (CP) - every APPN node has a control point from which LUs request network services. An APPN control point is similar to subarea PU.

• Transmission Group (TG) - links between APPN nodes.

APPN Network Nodes

APPN Networks• APPN networks are self-defining. NNs maintain a

distributed directory containing the characteristics and current status of each node and link.

• Central Directory Servers (CDSs) - Large networks have one or more CDS to hold the distributed directory.

• RTP Pipes - HPR groups sessions with the same Class of Service (COS) together into logical connections called RTP pipes. RTP pipes can be switched to a different path without affecting the sessions it carries.

APPN Networks• Management and Control Sessions - CP-CP sessions

between adjacent nodes• Interchange Node (ICN) - special kind of APPN NN

used to connect APPN and subarea networks. Supports hybrid VR-TG (virtual route based transmission group) communication and data flows.

• Dependent LU Server (DLUS) - special kind of APPN NN used to provide SSCP services to dependent LUs in a subarea network.

MNPS Example

MNPS Example• The endpoint of an interchange node (ICN) can

be either a transmission group (TG) or a virtual route (VR). Since it could be either, an RTP-capable path cannot be guaranteed, so IMS3 is not eligible for MNPS.

• If an LU were owned by EndNode1 (connected directly), the session with IMS1 is not recoverable because there is no HPR path to switch.

The Requirements for MNPS• All VTAMs with MNPS applications (CICS, IMS,

DB2) must be defined as APPN end nodes supporting RTP

• All VTAMs with MNPS applications must be connected to a MVS coupling facility that contains the VTAM structures

• MVS/ESA V5R2 or later• Coupling Facility Control Code (CFCC) Level 1 or

later• All VTAMs that own MNPS applications must be

V4R4 or later

Conclusions about MNPS• MNPS Fulfills the Sysplex Promise. When

the risks become trivial, the size of data centers and workloads will explode.Data Sharing DTR Persistent Sessions

• MNPS Will Cut Across Organizational Lines. Implementation may be difficult because support will cut across support groups.

Questions???