Business Continuity – Remote Replication

1. Business Continuity – Remote Replication

2. Remote Replication After completing this module, you will be able to: • Explain Remote Replication Concepts • Synchronous/Asynchronous • Connectivity Options • Discuss Host and Array based Remote Replication Technologies • Functionality • Differences • Considerations • Selecting the appropriate technology Business Continuity – Remote Replication

3. Remote Replication Concepts • Replica is available at a remote facility • Could be a few miles away or half way around the world • Backup and Vaulting are not considered remote replication • Synchronous Replication • Replica is identical to source at all times – Zero RPO • Asynchronous Replication • Replica is behind the source by a finite margin – Small RPO • Connectivity • Network infrastructure over which data is transported from source site to remote site Business Continuity – Remote Replication

4. 1 4 2 3 Data Write Data Acknowledgement Synchronous Replication • A write has to be secured on the remote replica and the source before it is acknowledged to the host • Ensures that the source and remote replica have identical data at all times • Write ordering is maintained at all times • Replica receives writes in exactly the same order as the source • Synchronous replication provides the lowest RPO and RTO • Goal is zero RPO • RTO is as small as the time it takes to start application on the remote site Disk Server Disk Business Continuity – Remote Replication

5. Max Writes MB/s Average Time Synchronous Replication • Response Time Extension • Application response time will be extended due to synchronous replication • Data must be transmitted to remote site before write can be acknowledged • Time to transmit will depend on distance and bandwidth • Bandwidth • To minimize impact on response time, sufficient bandwidth must be provided for at all times • Rarely deployed beyond 200 km Business Continuity – Remote Replication

6. Asynchronous Replication • Write is acknowledged to host as soon as it is received by the source • Data is buffered and sent to remote • Some vendors maintain write ordering • Other vendors do not maintain write ordering, but ensure that the replica will always be a consistent re-startable image • Finite RPO • Replica will be behind the Source by a finite amount • Typically configurable Disk 1 2 Server 3 4 Data Write Data Acknowledgement Disk Business Continuity – Remote Replication

7. Max Writes MB/s Average Time Asynchronous Replication • Response Time unaffected • Bandwidth • Need sufficient bandwidth on average • Buffers • Need sufficient buffers • Can be deployed over long distances Business Continuity – Remote Replication

8. Remote Replication Technologies • Host based • Logical Volume Manager (LVM) • Synchronous/Asynchronous • Log Shipping • Storage Array based • Synchronous • Asynchronous • Disk Buffered - Consistent PITs • Combination of Local and Remote Replication Business Continuity – Remote Replication

9. LVM Based Remote Replication • Duplicate Volume Groups at local and remote sites • All writes to the source Volume Group are replicated to the remote Volume Group by the LVM • Synchronous or Asynchronous Log Log Physical Volume 1 Physical Volume 3 Physical Volume 3 Physical Volume 1 Physical Volume 2 Physical Volume 2 Network Volume Group Volume Group Local Site Remote Site Business Continuity – Remote Replication

10. LVM Based Remote Replication • In the event of a network failure • Writes are queued in the log file • When the issue is resolved the queued writes are sent over to the remote • The maximum size of the log file determines the length of outage that can be withstood • In the event of a failure at the source site, production operations can be transferred to the remote site Business Continuity – Remote Replication

11. LVM Based Remote Replication • Advantages • Different storage arrays and RAID protection can be used at the source and remote sites • Standard IP network can be used for replication • Response time issue can be eliminated with asynchronous mode, with extended RPO • Disadvantages • Extended network outages require large log files • CPU overhead on host • For maintaining and shipping log files Business Continuity – Remote Replication

12. Host Based Log Shipping Logs • Offered by most DB Vendors • Advantages • Minimal CPU overhead • Low bandwidth • Standby Database consistent to last applied log IP Network Original Logs Stand By Business Continuity – Remote Replication

13. Array Based – Remote Replication • Replication performed by the array operating environment • Host CPU resources can be devoted to production operations instead of replication operations • Arrays communicate with each other via dedicated channels • ESCON, Fibre Channel or Gigabit Ethernet • Replicas are on different arrays • Primarily used for DR purposes • Can also be used for other BC operations Production Array Remote Array Network Distance Source Production Server Replica DR Server Business Continuity – Remote Replication

14. Write is received by the source array from host/server Write is transmitted by source array to the remote array Remote array sends acknowledgement to the source array Source array signals write complete to host/server Array Based – Synchronous Replication Network links Source Target Business Continuity – Remote Replication

15. Write is received by the source array from host/server Source array signals write complete to host/server Write is transmitted by source array to the remote array Remote array sends acknowledgement to the source array Array Based – Asynchronous Replication • No impact on response time • Extended distances between arrays • Lower bandwidth as compared to Synchronous Network links Source Target Business Continuity – Remote Replication

16. Array Based – Asynchronous Replication • Ensuring Consistency • Maintain write ordering • Some vendors attach a time stamp and sequence number with each of the writes, then ship the writes to the remote array and apply the writes to the remote devices in the exact order based on the time stamp and sequence numbers • Remote array applies the writes in the exact order they were received, just like synchronous • Dependent write consistency • Some vendors buffer the writes in the cache of the source array for a period of time (between 5 and 30 seconds) • At the end of this time the current buffer is closed in a consistent manner and the buffer is switched, new writes are received in the new buffer • The closed buffer is then transmitted to the remote array • Remote replica will contain a consistent, re-startable image on the application Business Continuity – Remote Replication

17. Array Based – Disk Buffered Consistent PITs • Local and Remote replication technologies can be combined to create consistent PIT copies of data on remote arrays • RPO usually in the order of hours • Lower Bandwidth requirements • Extended distance solution Business Continuity – Remote Replication

18. Remote Replica Local Replica Local Replica Source Extended Distance Consistent PIT SOURCE REMOTE • Create a Consistent PIT Local Replica on Source Array • Create a Remote Replica of this Local Replica • Optionally create another replica of the Remote replica on the remote array if needed • Repeat…as automation, link bandwidth, change rate permit Network Links Business Continuity – Remote Replication

19. Source Remote Replica Local Replica Local Replica Remote Replica Synchronous + Extended Distance Consistent PIT SOURCE BUNKER REMOTE • Synchronous replication between the Source and Bunker Site • Create consistent PIT Local Replica at bunker • Create Remote Replica of bunker Local Replica • Optionally create additional Local Replica at Target site from the Remote Replica if needed • Repeat…as automation, link bandwidth, change rate permit Sync Network Links Network Links Business Continuity – Remote Replication

20. Remote Replicas – Tracking Changes • Remote replicas can be used for BC Operations • Typically remote replication operations will be suspended when the remote replicas are used for BC Operations • During BC Operations changes will/could happen to both the source and remote replicas • Most remote replication technologies have the ability to track changes made to the source and remote replicas to allow for incremental re-synchronization • Resuming remote replication operations will require re-synchronization between the source and replica Business Continuity – Remote Replication

21. Primary Site Failure – Operations at Remote Site • Remote replicas are typically not available for use while the replication session is in progress • In the event of a primary site failure the replicas have to be made accessible for use • Create a local replica of the remote devices at the remote site • Start operations at the Remote site • No remote protection while primary site issues are resolved • After issue resolution at Primary Site • Stop activities at remote site • Restore latest data from remote devices to source • Resume operations at Primary (Source) Site Business Continuity – Remote Replication

22. Array Based – Which Technology • Synchronous • Is a must if zero RPO is required • Need sufficient bandwidth at all times • Application response time elongation will prevent extended distance solutions (rarely above 125 miles) • Asynchronous • Extended distance solutions with minimal RPO (order of minutes) • No Response time elongation • Generally requires lower Bandwidth than synchronous • Must design with adequate cache/buffer or sidefile/logfile capacity • Disk Buffered Consistent PITs • Extended distance solution with RPO in the order of hours • Generally lower bandwidth than synchronous or asynchronous Business Continuity – Remote Replication

23. Storage Array Based – Remote Replication • Network Options • Most vendors support ESCON or Fibre Channel adapters for remote replication • Can connect to any optical or IP networks with appropriate protocol converters for extended distances • DWDM • IP Networks • Some Vendors have native Gigabit Ethernet adapters which allows the array to be connected directly to IP Networks without the need for protocol converters Business Continuity – Remote Replication

24. Optical Channels ESCON Fibre Channel Gigabit Ethernet Optical Lambda λ Electrical Optical Dense Wavelength Division Multiplexing (DWDM) • DWDM is a technology that puts data from different sources together on an optical fiber with each signal carried on its own separate light wavelength (commonly referred to as a lambda or ). • Up to 32 protected and 64 unprotected separate wavelengths of data can be multiplexed into a light stream transmitted on a single optical fiber. Business Continuity – Remote Replication

25. Module Summary Key points covered in this module: • Remote Replication Concepts • Synchronous/Asynchronous • Connectivity Options • Host and Array based Remote Replication Technologies • Functionality • Differences • Considerations • Selecting the appropriate technology Business Continuity – Remote Replication

26. Check Your Knowledge  • What is a Remote Replica? • What are the possible uses of Remote Replicas? • What is the difference between Synchronous and Asynchronous Replication? • Discuss one host based remote replication technology? • Discuss one array based remote replication technology? • What are differences in the bandwidth requirements between the array remote replication technologies discussed in this module? Business Continuity – Remote Replication