Business Continuity: Remote Replication

1. Business Continuity: Remote Replication Module 4.4

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 • SONET • 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. STM-16 STM-1 STM-16 SDH Synchronous Optical Network (SONET) • SONET is Time Division Multiplexing (TDM) technology where traffic from multiple subscribers is multiplexed together and sent out onto the SONET ring as an optical signal • Synchronous Digital Hierarchy (SDH) similar to SONET but is the European standard • SONET/SDH, offers the ability to service multiple locations, its reliability/availability, automatic protection switching, and restoration Business Continuity – Remote Replication

26. Rated Bandwidth Business Continuity – Remote Replication

27. 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

28.  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

29. Apply Your Knowledge… Upon completion of this topic, you will be able to: • Enumerate EMC’s Remote Replication Solutions for the Symmetrix and CLARiiON arrays • Describe EMC’s SRDF/Synchronous Replication Solution • Describe EMC’s MirrorView/A Replication Solution Business Continuity – Remote Replication

30. EMC – Remote Replication Solutions • EMC Symmetrix Arrays • EMC SRDF/Synchronous • EMC SRDF/Asynchronous • EMC SRDF/Automated Replication • EMC CLARiiON Arrays • EMC MirrorView/Synchronous • EMC MirrorView/Asynchronous Business Continuity – Remote Replication

31. EMC SRDF/Synchronous - Introduction • Array based Synchronous Remote Replication technology for EMC Symmetrix Storage Arrays • Facility for maintaining real-time physically separate mirrors of selected volumes • SRDF/Synchronous uses special Symmetrix devices • Source arrays have SRDF R1 devices • Target arrays have SRDF R2 devices • Data written to R1 devices are replicated to R2 devices • SRDF uses dedicated channels to send data from source to target array • ESCON, Fibre Channel or Gigabit Ethernet are supported • SRDF is available in both Open Systems and Mainframe environments Business Continuity – Remote Replication

32. SRDF Source and Target Volumes • SRDF R1 and R2 Volumes can have any local RAID Protection • E.g. Volumes could have RAID-1 or RAID-5 protection • SRDF R2 volumes are in a Read Only state when remote replication is in effect • Changes cannot be made to the R2 volumes • SRDF R2 volumes are accessed under certain circumstances • Failover – Invoked when the primary volumes become unavailable • Split – Invoked when the R2 volumes need to be concurrently accessed for BC operations Business Continuity – Remote Replication

33. Target Host Source Host ChannelDirector (CD) ChannelDirector (CD) ChannelDirector (CD) ChannelDirector (CD) Remote LinkDirector (RLD) Remote LinkDirector (RLD) Global Cache Director Global Cache Director Remote LinkDirector (RLD) Remote LinkDirector (RLD) DiskDirector (DD) DiskDirector (DD) DiskDirector (DD) DiskDirector (DD) Symmetrix Containing Target (R2) Volumes Symmetrix Containing Source (R1) Volumes SRDF/Synchronous 1. Write received by Symmetrix containing Source volume 2. Source Symmetrix sends write data to Target 3. Target Symmetrix sends acknowledgement to Source 4. Write complete sent to host 1 4 2 3 • Application does not receive I/O acknowledgement until data is received and acknowledged by remote Symmetrix • Write completion time is extended - No impact on Reads • Most often used in campus solutions Business Continuity – Remote Replication

34. Before RW RO SourceVolume Target Volume SRDF Operations - Failover • Purpose – Make Target Volumes Read Write • Source Volume status is changed to Read Only • SRDF Link is suspended RO RW After SourceVolume Target Volume Business Continuity – Remote Replication

35. Before RO RW SourceVolume Target Volume RW RO After SourceVolume Target Volume sync SRDF Operations - Failback • Makes target volume Read Only, resumes link, synchronize R2 to R1, and write enables source volume Business Continuity – Remote Replication

36. Before RW RO SourceVolume Target Volume RW RW After SourceVolume Target Volume SRDF Operations - Split • Enables read and write operations on both source and target volumes • Suspends replication Business Continuity – Remote Replication

37. RW RO RW RO SourceVolume Target Volume SourceVolume Target Volume Restore Establish SRDF Operations – Establish/Restore • Establish - Resume SRDF operation retaining data from source and overwriting any changed data on target • Restore - SRDF operation retaining data on target and overwriting any changed data on source Business Continuity – Remote Replication

38. EMC CLARiiON MirrorView/A Overview • Optional storage system software for remote replication on EMC CLARiiON arrays • No host cycles used for data replication • Provides a remote image for disaster recovery • Remote image updated periodically - asynchronously • Remote image cannot be accessed by hosts while replication is active • Snapshot of mirrored data can be host-accessible at remote site • Mirror topology (connecting primary array to secondary arrays) • Direct connect and switched FC topology supported • WAN connectivity supported using specialized hardware Business Continuity – Remote Replication

39. MirrorView/A Terms • Primary storage system • Holds the local image for a given mirror • Secondary storage system • Holds the local image for a given mirror • Bidirectional mirroring • A storage system can hold local and remote images • Mirror Synchronization • Process that copies data from local image to remote image • MirrorView Fractured state • Condition when a Secondary storage system is unreachable by the Primary storage system Business Continuity – Remote Replication

40. MirrorView/A Configuration • MirrorView/A Setup • MirrorView/A software must be loaded on both Primary and Secondary storage system • Remote LUN must be exactly the same size as local LUN • Secondary LUN does not need to be the same RAID type as Primary • Reserved LUN Pool space must be configured • Management via Navisphere Manager and CLI Business Continuity – Remote Replication

41. MirrorView/A – Initial Synchronization Primary Image Secondary Image D A B’ E’ E A B C E F B C D F Host Tracking DeltaMap 0 0 1 0 0 1 0 0 Snapshot Transfer DeltaMap 1 0 1 0 1 0 1 0 0 1 0 1 E RLP MAP MAP Business Continuity – Remote Replication

42. MirrorView/A – Update Primary Image Secondary Image E” E’ D A E A B’ C E’ F B C D F A’ B’ Host Tracking DeltaMap Transfer DeltaMap 0 0 1 0 0 0 0 1 Snapshot Transfer DeltaMap Tracking DeltaMap 1 0 0 0 0 1 0 0 E’ B E RLP MAP MAP Business Continuity – Remote Replication

43. MirrorView/A –Promotion (Update Failure) Primary Image Secondary Image Primary Image B’ E” D A E B’ C E’ F’ C D F B A’ Host Promote Secondary Transfer DeltaMap 0 0 0 0 0 1 Snapshot Tracking DeltaMap 1 0 0 0 1 0 1 E’ B RLP MAP MAP Business Continuity – Remote Replication

44. Consistency Groups • Group of secondary images treated as a unit • Local LUNs must all be on the same CLARiiON • Remote LUNs must all be on the same CLARiiON • Operations happen on all LUNs at the same time • Ensures a restartable image group Business Continuity – Remote Replication