Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Local Replication Chapter 13(9.2) ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Chapter Objective After completing this chapter you will be able to: Discuss local replication and the possible uses of local replicas Explain consistency considerations when replicating file systems and databases Discuss host and array based replication technologies Functionality Differences Considerations Selecting the appropriate technology ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Lesson: Local Replica and Data Consistency Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Lesson: Local Replica and Data Consistency Upon completion of this lesson, you will be able to: Define local replication Discuss the possible uses of local replicas Explain replica considerations such as Recoverability and Consistency Describe how consistency is ensured in file system and database replication Explain Dependent write principle ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. What is Replication Replica - An exact copy Replication - The process of reproducing data Local replication - Replicating data within the same array or the same data center REPLICATION Source Replica (Target) ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Possible Uses of Local Replicas Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Possible Uses of Local Replicas Alternate source for backup Fast recovery Decision support Testing platform Data Migration ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Replication Considerations Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Replication Considerations Types of Replica: choice of replica tie back into RPO Point-in-Time (PIT) non zero RPO Continuous near zero RPO What makes a replica good Recoverability/Re-startability Replica should be able to restore data on the source device Restart business operation from replica Consistency Ensuring consistency is primary requirement for all the replication technologies ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Understanding Consistency Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Understanding Consistency Consistency is required to ensure the usability of replica Consistency can be achieved in various ways: For file Systems Offline: Un-mount file system Online: Flush host buffers For Databases Offline: Shutdown database Online: Database in hot backup mode Dependent Write I/O Principle By Holding I/Os ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

File System Consistency: Flushing Host Buffer Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. File System Consistency: Flushing Host Buffer Application File System Data Sync Daemon Memory Buffers Logical Volume Manager Physical Disk Driver Source Replica ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Database Consistency: Dependent write I/O Principle Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Database Consistency: Dependent write I/O Principle Dependent Write: A write I/O that will not be issued by an application until a prior related write I/O has completed A logical dependency, not a time dependency Inherent in all Database Management Systems (DBMS) e.g. Page (data) write is dependent write I/O based on a successful log write Necessary for protection against local outages Power failures create a dependent write consistent image A Restart transforms the dependent write consistent to transitionally consistent i.e. Committed transactions will be recovered, in-flight transactions will be discarded ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Database Consistency: Dependent Write I/O Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Database Consistency: Dependent Write I/O Source Replica Source Replica 1 1 1 2 2 2 3 3 3 3 4 4 4 4 C C D Consistent Inconsistent ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Database Consistency: Holding I/O Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Database Consistency: Holding I/O Source Replica 1 1 5 5 2 2 3 3 4 4 Consistent ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Lesson Summary Key points covered in this lesson: Possible uses of local replicas Alternate source for backup Fast recovery Decision support Testing platform Data Migration Recoverability and Consistency File system and database replication consistency Dependent write I/O principle ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Lesson: Local Replication Technologies Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Lesson: Local Replication Technologies Upon completion of this lesson, you will be able to: Discuss Host and Array based local replication technologies Options Operation Comparison ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Local Replication Technologies Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Local Replication Technologies Host based Logical Volume Manager (LVM) based mirroring File System Snapshot Storage Array based Full volume mirroring Pointer based full volume replication Pointer based virtual replication ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Host Based Replication: LVM Based Mirroring Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Host Based Replication: LVM Based Mirroring Physical Volume 1 Host Logical Volume Logical Volume Physical Volume 2 ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. File System Snapshot Pointer-based replica Uses Copy on First Write principle Uses bitmap and block map Bitmap: Used to track blocks that have changed on the production/source FS after creation of snap – initially all zero Block map: Used to indicate block address from which data is to be read when the data is accessed from the Snap FS – initially points to production/source FS Requires a fraction of the space used by the original FS Implemented by either FS itself or by LVM ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

File System Snapshots – How it Works Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. File System Snapshots – How it Works Write to Production FS Snap FS Metadata Prod FS BLK Bit 1-0 1-0 Metadata 2-0 2-0 1 Data a 3-0 3-2 3-1 3-0 2 Data b 4-1 4-0 4-0 4-1 3 Data C c New writes 4 Data D d 1 Nodata 1 Data d 1 no data 2 Data c 2 no data 3 no data N Data N 4 no data ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

File System Snapshots – How it Works Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. File System Snapshots – How it Works Reads from snap FS Consult the bitmap If 0 then direct read to the production FS If 1 then go to the block map get the block address and read data from that address Snap FS Metadata Prod FS BLK Bit Metadata 1-0 1-0 1 Data a 2-0 2-0 2 Data b 3-2 3-1 3 Data C 4-1 4-1 4 Data D 1 Data d 1 Nodata 2 Data c N Data N 3 no data 4 no data ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Host Based Replication: Limitations Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Host Based Replication: Limitations LVM based replicas add overhead on host CPUs If host volumes are already storage array LUNs then the added redundancy provided by LVM mirroring is unnecessary The devices will have some RAID protection already Host based replicas can be usually presented back to the same server Keeping track of changes is a challenge after the replica has been created ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Storage Array Based Local Replication Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Storage Array Based Local Replication Replication performed by the Array Operating Environment Replicas are on the same array Types of array based replication Full-volume mirroring Pointer-based full-volume replication Pointer-based virtual replication Array Source Replica Production Server ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT BC Server

Full Volume Mirroring: Attached Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Full Volume Mirroring: Attached Target is a full physical copy of the source device Target is attached to the source and data from source is copied to the target Target is unavailable while it is attached Target device is as large as the source device Good for full backup, decision support, development, testing and restore to last PIT Attached Read/Write Not Ready Source Target Array ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Full Volume Mirroring: Detached Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Full Volume Mirroring: Detached After synchronization, target can be detached from the source and made available for BC operations PIT is determined by the time of detachment After detachment, re-synchronization can be incremental Detached - PIT Read/Write Read/Write Source Target Array ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Full Volume Mirroring: Source and Target Relationship Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Full Volume Mirroring: Source and Target Relationship Attached/ Synchronization Detached Resynchronization Source = Target Source ≠ Target Source = Target ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Pointer Based Full Volume Replication Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Pointer Based Full Volume Replication Provide full copy of source data on the target Target device is made accessible for business operation as soon as the replication session is started Point-in-Time is determined by time of session activation Two modes Copy on First Access (deferred) Full Copy mode Target device is at least as large as the source device ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Copy on First Access Mode: Deferred Mode Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Copy on First Access Mode: Deferred Mode Write to Source Read/Write Read/Write Source Target Write to Target Read/Write Read/Write Source Target Read from Target Read/Write Read/Write Source ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT Target

Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Full Copy Mode On session start, the entire contents of the Source device is copied to the Target device in the background Most vendor implementations provide the ability to track changes: Made to the Source or Target Enables incremental re-synchronization ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Pointer Based Virtual Replication Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Pointer Based Virtual Replication Targets do not hold actual data, but hold pointers to where the data is located Target requires a small fraction of the size of the source volumes A replication session is setup between source and target devices Target devices are accessible immediately when the session is started At the start of the session the target device holds pointers to data on source device Typically recommended if the changes to the source are less than 30% ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Virtual Replication: Copy on First Write Example Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Virtual Replication: Copy on First Write Example Target Virtual Device Source Save Location ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Tracking Changes to Source and Target Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Tracking Changes to Source and Target Changes will/can occur to the Source/Target devices after PIT has been created How and at what level of granularity should this be tracked Too expensive to track changes at a bit by bit level Would require an equivalent amount of storage to keep track Based on the vendor some level of granularity is chosen and a bit map is created (one for source and one for target) For example one could choose 32 KB as the granularity If any change is made to any bit on one 32KB chunk the whole chunk is flagged as changed in the bit map For 1GB device, map would only take up 32768/8/1024 = 4KB space ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Tracking Changes to Source and Target: Bitmap Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Tracking Changes to Source and Target: Bitmap Source At PIT Target Source 1 1 1 After PIT… Target 1 1 1 For resynchronization/restore Logical OR 1 1 1 1 1 = unchanged 1 = changed ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Restore/Restart Operation Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Restore/Restart Operation Source has a failure Logical Corruption Physical failure of source devices Failure of Production server Solution Restore data from target to source The restore would typically be done incrementally Applications can be restarted even before synchronization is complete -----OR------ Start production on target Resolve issues with source while continuing operations on target After issue resolution restore latest data on target to source ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Restore/Restart Considerations Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Restore/Restart Considerations Before a Restore Stop all access to the Source and Target devices Identify target to be used for restore Based on RPO and Data Consistency Perform Restore Before starting production on target Identify Target to be used for restart Create a “Gold” copy of Target As a precaution against further failures Start production on Target ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Restore/Restart Considerations (cont.) Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Restore/Restart Considerations (cont.) Pointer based Full Volume Replicas Restores can be performed to either the original source device or to any other device of like size Restores to the original source could be incremental in nature Restore to a new device would involve a full synchronization Pointer Based virtual Replicas Restores can be performed to the original source or to any other device of like size as long as the original source device is healthy Target only has pointers Pointers to source for data that has not been written to after PIT Pointers to the “save” location for data was written after PIT Thus to perform a restore to an alternate volume the source must be healthy to access data that has not yet been copied over to the target ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Array Replicas: Which Technology? Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Array Replicas: Which Technology? Factor Full-volume mirroring Pointer-based full-volume replication Pointer-based virtual replication Performance impact on source No impact CoFA mode -some impact Full copy – no impact High impact Size of target At least same as the source Small fraction of the source Accessibility of source for restoration Not required CoFA mode – required Full copy – not required Required Accessibility to target Only after synchronization and detachment from the source Immediately accessible ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Creating Multiple Replicas Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Creating Multiple Replicas Target Devices 06:00 A.M. Source 12:00 P.M. Point-In-Time 06:00 P.M. 12:00 A.M. : 12 : 01 : 02 : 03 : 04 : 05 : 06 : 07 : 08 : 09 : 10 : 11 : 12 : 01 : 02 : 03 : 04 : 05 : 06 : 07 : 08 : 09 : 10 : 11 : A.M. P.M. ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Local Replication Management: Array Based Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Local Replication Management: Array Based Replication management software residing on storage array Provides an interface for easy and reliable replication management Two types of interface: CLI GUI ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Lesson Summary Key points covered in this lesson: Replication technologies Host based LVM based mirroring File system snapshot Array based Full volume mirroring Pointer-based full volume copy Pointer-based virtual replica ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Exercise 1 Click the attached file ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Exercise 2 Click the attached file ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Chapter Summary Key points covered in this chapter: Definition and possible use of local replicas Consistency considerations when replicating file systems and databases Host based replication LVM based mirroring, File System Snapshot Storage array based replication Full volume mirroring, Pointer based full volume and virtual replication Choice of technology ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Concept in Practice – EMC Local Replication Solutions Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. Concept in Practice – EMC Local Replication Solutions EMC Symmetrix Arrays EMC TimeFinder/Clone Full volume replication EMC TimeFinder/Mirror Full volume mirroring EMC TimeFinder/SNAP Pointer based replication EMC CLARiiON Arrays EMC SnapView Clone EMC SnapView Snapshot ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

EMC Local Replication Video Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved. EMC Local Replication Video ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

Copyright © 2009 EMC Corporation. Do not Copy - All Rights Reserved.  Check Your Knowledge Describe the uses of a local replica in various business operations. How can consistency be ensured when replicating a database? What are the differences among full volume mirroring and pointer based replicas? What is the key difference between full copy mode and deferred mode? What are the considerations when performing restore operations for each array replication technology? ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT

ISMDR:BEIT:VIII:chap9.2:Madhu N:PIIT