Click to add text Introduction to the new mainframe: Large-Scale Commercial Computing © Copyright IBM Corp., All rights reserved. Chapter 2: Capacity

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 2 Chapter objectives At the end of this chapter you should be able to describe: Mixed workloads SLA (Service Level Agreement) PR/SM and LPAR Parallel Sysplex Storage concepts and management Measuring capacity

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 3 Definition of Capacity Capacity has several definitions: 1. The potential or suitability for holding, storing, or accommodating (access) data 2. The facility or power to produce, perform, deploy or, simply process (compute)

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 4 Elements required for capacity (1/2) Any computer system, performs work in the following stages: 1.Load a program from a storage device, normally a disk, to central storage 2.Process the instructions in the program 3.Load any required data from disk or tape into central storage 4.Process the data and send the results to the desired end point

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 5 Elements required for capacity (2/2) The components that perform these steps are:  Processors  Central storage (RAM)  Access input/output storage (for example disk or tape)  Also the network to these devices has to be considered need to be planned for: capacity estimation & planning

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 6 Considerations: Many servers Few Servers - Many servers (small servers) :  Data retention ? Data currency  Locking across servers ?  Connectivity ? And Lots of communication Few servers (IBM System z):  Large volumes of data: best in 1 place  No rewritting needed of applications  1 total system (Single System Image)

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 7 Why a Mixed Workload Unlikely that in a commercial environment, one program could keep a processor fully utilized over a long period of time. Example of a mixed workload, running jobs for  Online customers,  Online in-house users and  Batch work on the same system.

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 8 Service Level Agreement A Service Level Agreement (SLA) is an agreement between a service provider and a recipient, generally the server organization and a business unit. SLAs are the baseline for capacity, availability and performance measurements and ratings. Example: 95% of ATM transactions are completed in less than one second. With a defined load..i.e. Transactions/sec 90% of daily reports are completed by 6 A.M.

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 9 Managing the system to the SLA  Managing CPU  Managing Disk  Storage concepts (the address space..Virtual memory) -> see next slide  Real storage mangement

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 10 A Virtual Address space  The „Line“ 24 Bit systems  The „Bar“ 31 Bit systems

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 11 Architecture, running work & capacity  Program Status Word (PSW)  Interrupts Machine check Restart Program Check I/O Supervisor call (SVC) External  Supervisor call  Selection of work to run on a CP-scheduler  Dispatching priority  CP utilization balance

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 12 Several servers on 1 physical machine  LPAR  Planning for downtime Software- updates, repair, replace Hardware- replace, repair, maintain

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 13 IBM System z – Parallel Sysplex ESCON/FICON Coupling Facility SYSPLEX Timer Shared Data Z9 BC Z9 EC Z9 BC Parallel Sysplex

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 14 Measurements  Central Processor usage  Central storage usage  Access to disk storage

Introduction to the new mainframe © Copyright IBM Corp., All rights reserved. 15 Summary Capacity  Complex when you are : In a mixed workload On a large-scale commercial environment  Different workloads  different requirements  well defined set of SLAs needed  SLAs are also helpfull for: Measurement of capacity bottlenecks the planning of capacity upgrades.