Remote Replication Chapter 14(9.3) ISMDR:BEIT:VIII:chap9.3:Madhu N:PIIT1

- 2 Chapter Objective After completing this chapter, you will be able to: Explain remote replication technologies – Synchronous and asynchronous Discuss host and array based remote replication – Functionality – Differences – Selecting the appropriate technology Discuss network options for remote replication

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 3 What is Remote Replication? Replica is created at remote site – Addresses risk associated with regionally driven outages – Could be a few miles away or half way around the globe Modes of remote replication (based on RPO requirement) – Synchronous Replication – Asynchronous Replication Source site Remote site

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 4 Synchronous Replication A write must be committed to the source and remote replica before it is acknowledged to the host Ensures source and remote replica have identical data at all times – Write ordering is maintained 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 target site Data Write Data Acknowledgement Host Target Source

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 5 Synchronous Replication: Bandwidth Requirement Response Time Extension – Application response time will be extended Data must be transmitted to target 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 at all times Rarely deployed beyond 200 km Time Writes MB/s Required bandwidth Typical workload Max

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 6 Asynchronous Replication Write is committed to the source and immediately acknowledged to the host Data is buffered at the source and transmitted to the remote site later – 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 Data Write Data Acknowledgement Host Target Source

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 7 Asynchronous Replication: Bandwidth Requirement Response time unaffected Bandwidth – Need average bandwidth Buffers – Need sufficient buffers Can be deployed over long distances Average Time Writes MB/s Required bandwidth Typical workload

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 8 Remote Replication Technologies Host based – Logical Volume Manager (LVM) based Support both synchronous and asynchronous mode – Log Shipping Storage Array based – Support both synchronous and asynchronous mode – Disk Buffered - Consistent PITs Combination of Local and Remote Replication

ISMDR:BEIT:VIII:chap9.3:Madhu N:PIIT - 9 LVM Based Duplicate Volume Groups at source and target sites – All writes to the source Volume Group are replicated to the target Volume Group by the LVM – Can be synchronous or asynchronous mode In the event of a network failure – Writes are queued in the log file and sent to target when the issue is resolved – Size of the log file determines length of outage that can be withstood Upon failure at source site, production can be transferred to target site IP

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 10 LVM Based – Advantages and Limitations Advantages – Different storage arrays and RAID protection can be used at the source and target sites – Response time issue can be eliminated with asynchronous mode, with extended RPO Limitations – Extended network outages require large log files – CPU overhead on host

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 11 Host Based Log Shipping Offered by most database Vendors Advantages – Minimal CPU overhead – Low bandwidth requirement – Standby Database consistent to last applied log Original Logs Stand By Logs IP

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 12 Source Array Storage 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 business operations Target Array Distance Source Replica DR Server Production Server IP/FC Network

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 13 Array Based – Synchronous Replication Network links Write is received by the source array from host/serverWrite is transmitted by source array to the target arrayTarget array sends acknowledgement to the source arraySource array signals write complete to host/server SourceTarget

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 14 Array Based – Asynchronous Replication No impact on response time Extended distances between arrays Lower bandwidth as compared to Synchronous Write is received by the source array from host/server Write is transmitted by source array to the target arraySource array signals write complete to host/server Target array sends acknowledgement to the source array Network links SourceTarget

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 15 Asynchronous Replication: Ensuring Consistency Maintain write ordering – Some vendors attach a time stamp and sequence number with each write, then send the writes to remote array – Apply these writes to the remote devices in exact order based on the time stamp and sequence numbers 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 current buffer is closed in a consistent manner and the buffer is switched, new writes are received in the new buffer – Closed buffer is then transmitted to the remote array – Remote replica will contain a consistent, re-startable image on the application

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 16 Array Based – Disk Buffered Replication Local and Remote replication technologies can be combined to create consistent PIT copies of data on target arrays RPO usually in the order of hours Lower Bandwidth requirements Extended distance solution Source Storage Array Target Storage Array Local Replica Remote Replica Local Replica Source Host Source Data

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 17 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 business 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

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 18 Array Based – Which Technology? Synchronous – Is a must if zero RPO is required – Need sufficient bandwidth at all times – 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 capacity Disk buffered – Extended distance solution with RPO in the order of hours – Require lower bandwidth than synchronous or asynchronous

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 19 Three Site Replication Eliminates disadvantages of two site replication – Single site disaster leads to a window when there is no DR protection Data replicated to two remote sites Implemented in two ways – Three Site Cascade/Multi-hop – Three Site Triangle/Multi-target

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 20 Three Site Replication – Cascade/Multi-hop Synchronous + Disk Buffered Synchronous + Asynchronous Bunker Site Remote Site Local Replica Remote Replica Local Replica Source Data Synchronous Remote Replica Disk Buffered Source Site Bunker Site Remote Site Local Replica Remote Replica Local Replica Source Data Synchronous Remote Replica Asynchronous Source Site

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 21 Three Site Replication – Triangle/Multi- target Asynch with Differential Resynch SOURCE REMOTE BUNKER Sync Async SAN

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 22 SAN Based Remote Replication Replicate from one storage array to any other storage array over the SAN/WAN – Implement tiered storage – Data migration – Remote vaulting Heterogeneous arrays support No impact to servers or the LAN Hitachi EMC Symmetrix EMC CLARiiON HP IBM SAN/WAN

ISMDR:BEIT:VIII:chap9.3:Madhu N:PIIT - 23 SAN Based Replication: Terminologies Control Array: Array responsible for the replication operations – Control Device: Device on controlling array to/from which data is being replicated Remote Array: Array to/from which data is being replicated – Remote Device: Device on remote array to/from which data is being replicated Operation – Push: Data is pushed from control array to remote array – Pull: Data is pulled to the control array from remote array Control Array Remote Array PUSH PULL Control Device Remote Device C C SAN/WAN

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 24 Network Options for Remote Replication A dedicated or a shared network must be in place for remote replication – Use ESCON or FC for shorter distance – For extended distances, an optical or IP network must be used – Example of optical network: DWDM and SONET Protocol converters may require to connect ESCON or FC adapters from the arrays to these networks – Native GigE adapters allows array to be connected directly to IP Networks

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 25 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 Up to 32 protected and 64 unprotected separate wavelengths of data can be multiplexed into a light stream transmitted on a single optical fiber ESCON Fibre Channel Gigabit Ethernet Optical Channels Optical Electrical Optical Lambda λ

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 26 Synchronous Optical Network (SONET) SONET is Time Division Multiplexing (TDM) technology Traffic from multiple subscribers is multiplexed together and sent out onto 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 SDH STM-1 STM-16 SONET OC3 OC48

ISMDR:BEIT:VIII:chap9.3:Madh u N:PIIT - 27 Chapter Summary Key points covered in this chapter: Modes of remote replication – Synchronous and asynchronous mode Host based remote replication – LVM based and log shipping Array based remote replication – Synchronous, asynchronous and disk buffered – Three site replication – SAN based remote replication Network options for remote replication