© Logicalis Group HA options Cross Site Mirroring (XSM) and Orion Jonathan Woods

XSM - Overview New ‘Page level’ replication option Native to OS/400 Ultimate protection iASP to iASP via LAN/WAN Sync and Async options High bandwidth Another ‘comms’ option for an HA solution

High level XSM Schematic High bandwidth WAN iASP *SYSBAS XSM Replication  * SYSBAS not replicated  Clustering required to switch device resource group  Orion manages clustering Orion Replication Clustering heartbeat

XSM - detail Initial synchronisation goes via LAN/WAN Could be lengthy for big disk 3.5hrs for 100GB over 100Mbps If communications fail a full re-sync is required for target disk User operations can continue Timeout after comms failure can be set After timeout replication suspended Sync option also needs high bandwidth to keep source response times good Async can help relieve this problem

Sync versus Async Synchronous replication Target system has to acknowledge disk write back to source system before source app continues Asynchronous replication Source system application continues regardless off target disk write Either source or target transaction queue is required

The Availability Building Blocks Data Resiliency Data Replication Data Availability Copy of data not application Hardware Protection Raid 5 and Disk Mirroring Data Resilience Physical disk protection Application Resilience Application Failover High Availability Fast manual recovery Transaction Integrity Journaling Disaster Recovery Protection from data loss (in case of memory crash) Clustering Failure Detection, Auto Failover Continuous Availability Application users unaffected Clustering Failure Detection, Auto Failover

HA comms options summary Switched HSL bus disk (local HA only) OS/400 Remote journaling – sync or async Orion replication (from journal) – async + reduced bandwidth Switched disk replication async or sync (ESS-Shark) XSM replication – async or sync

OS/400 internals *FILE PF*JRN Application Main storage Disk Users Proximity to App 1. Main storage is closest 2. OS/400 Journaling 3. Disk subsystem XSM Replication Orion/Remote JRN Replication ESS/Shark Replication

Conclusion - pure iSeries If Synchronous replication required, XSM is the best choice there is If lower cost of async is attractive then Journal based replication has more benefits: Suspend/resume with no re-sync Initial Sync via tape could be quicker Easy backup off target option Orion relevant either way Replicates *SYSBAS Manages clustering