Dell EMC SRDF Introduction

Dell EMC SRDFIntroductionRev 01September 2019

Copyright 2019 Dell Inc. or its subsidiaries. All rights reserved.Dell believes the information in this publication is accurate as of its publication date. The information is subject to change without notice.THE INFORMATION IN THIS PUBLICATION IS PROVIDED “AS-IS.” DELL MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KINDWITH RESPECT TO THE INFORMATION IN THIS PUBLICATION, AND SPECIFICALLY DISCLAIMS IMPLIED WARRANTIES OFMERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. USE, COPYING, AND DISTRIBUTION OF ANY DELL SOFTWARE DESCRIBEDIN THIS PUBLICATION REQUIRES AN APPLICABLE SOFTWARE LICENSE.Dell Technologies, Dell, EMC, Dell EMC and other trademarks are trademarks of Dell Inc. or its subsidiaries. Other trademarks may be the propertyof their respective owners. Published in the USA.Dell EMCHopkinton, Massachusetts 01748-91031-508-435-1000 In North America 1-866-464-7381www.DellEMC.com2Dell EMC SRDF Introduction

CONTENTSFigures7Tables9Chapter 1PREFACE11Introduction13What is SRDF?. 14Disaster recovery.14High availability.16Data migration. 17SRDF concepts.18SRDF device pairs.18SRDF device states.22Invalid tracks in SRDF pairs. 27SRDF groups.28Dynamic devices. 29SRDF modes of operation. 30SRDF consistency. 32Director boards, links, and ports.33Chapter 2Disaster recovery352-site configurations. 363-site configurations. 39Concurrent SRDF solutions. 41Cascaded SRDF solutions. 42SRDF/Star solutions. 434-site configurations. 514-site FBA configurations. 514-site mainframe configurations (SRDF/SQAR). 52SRDF recovery scenarios.54Planned failover (SRDF/S). 54Unplanned failover . 55Failback to the primary array. 56Recovery for a large number of invalid tracks. 56Temporary link loss. 56Permanent link loss (SRDF/A). 56SRDF/A session cleanup.56Failback from R2 devices. 57Chapter 3High availability59SRDF/Metro .60SRDF/Metro life cycle. 62SRDF/Metro resilience. 63Device Bias. 63Array Witness. 64Virtual Witness (vWitness). 65Dell EMC SRDF Introduction3

ContentsWitness negotiation and selection.66Witness failure scenarios.67Mobility ID with ALUA. 68Disaster recovery facilities.69Deactivate SRDF/Metro. 70SRDF/Metro restrictions. 71Chapter 4Data migration73Introduction to data migration using SRDF. 74Non-disruptive migration.74Migration from VMAX array. 74Migration from VMAX All Flash or VMAX3. 75Migrating data with concurrent SRDF. 77Replacing R1 devices with new R1 devices.77Replacing R2 devices with new R2 devices. 79Replacing R1 and R2 devices with new R1 and R2 devices. 80Migration-only SRDF. 81Device Migration operations requirements .82Chapter 5SRDF I/O operations83SRDF write operations. 84Write operations in synchronous mode. 84Write operations in asynchronous mode.84Cycle switching in asynchronous mode. 86Write operations in cascaded SRDF. 89SRDF read operations. 90Read operations if R1 local copy fails. 90Read operations from R2 devices.90SRDF/A resilience and performance features.91Tunable cache. 91SRDF/A cache data offloading . 91Transmit Idle. 92Write folding. 92Write pacing .92Chapter 6Interfamily compatibility95Overview. 96SRDF supported features. 96Chapter 7Management tools99Solutions Enabler.100Unisphere. 100SRDF/TimeFinder Manager for IBM i.101Mainframe management tools. 102Mainframe Enablers.102Geographically Dispersed Disaster Restart (GDDR). 103Chapter 8More information105Solutions Enabler CLI. 106Unisphere. 106Mainframe Enablers.106GDDR. 1064Dell EMC SRDF Introduction

ContentsSRDF/TimeFinder Manager for IBM i. 106SRDF/Metro vWitness. 106SRDF Interfamily Compatibility. 106Storage arrays. 107Dell EMC SRDF Introduction5

Contents6Dell EMC SRDF Introduction

2728293031323334353637Data replicated to one additional array. 14Data replicated to two arrays simultaneously.15SRDF/Metro example.16Migration example. 17R1 and R2 devices .18R11 device in concurrent SRDF. 19R21 device in cascaded SRDF. 20R22 devices in cascaded and concurrent SRDF/Star. 21Host interface view and SRDF view of states. 22Concurrent SRDF topology.41Cascaded SRDF topology.42Concurrent SRDF/Star. 44Concurrent SRDF/Star with R22 devices. 45Cascaded SRDF/Star.46R22 devices in cascaded SRDF/Star.47Concurrent SRDF/Star with GDDR.48Cascaded SRDF/Star with GDDR. 49SRDF 4-site FBA configuration.51SRDF/SQAR with Autoswap environment. 52Planned failover: before personality swap. 54Planned failover: after personality swap. 55Failover to Site B, Site A and production host unavailable.55SRDF/Metro.60SRDF/Metro life cycle. 62SRDF/Metro Array Witness and groups.64SRDF/Metro vWitness vApp and connections. 65SRDF/Metro Witness single failure scenarios. 67SRDF/Metro Witness multiple failure scenarios.68Disaster recovery for SRDF/Metro.69Migrating data and replacing the original primary array (R1). 78Migrating data and removing the original secondary array (R2). 79Migrating data and replacing the original primary (R1) and secondary (R2) arrays. 80Write I/O flow: simple synchronous SRDF. 84SRDF/A SSC cycle switching – multi-cycle mode. 86SRDF/A SSC cycle switching – legacy mode.87SRDF/A MSC cycle switching – multi-cycle mode. 88Write commands to R21 devices. 89Dell EMC SRDF Introduction7

Figures8Dell EMC SRDF Introduction

TABLES123456789SRDF pair states. 23R1 device accessibility.25R2 device accessibility. 25Possible SRDF device and link state combinations . 26SRDF 2-site configurations. 36SRDF multi-site solutions .39Limitations of the migration-only mode . 81SRDF features by hardware platform/operating environment. 96Unisphere tasks. 100Dell EMC SRDF Introduction9

Tables10Dell EMC SRDF Introduction

PREFACEAs part of an effort to improve its product lines, Dell EMC periodically releases revisions of itssoftware and hardware. Therefore, some functions described in this document might not besupported by all versions of the software or hardware currently in use. The product release notesprovide the most up-to-date information on product features.Contact your Dell EMC technical support professional if a product does not function properly ordoes not function as described in this document.Note: This document was accurate at publication time. Go to Dell EMC Online Support(https://support.emc.com) to ensure that you are using the latest version of this document.PurposeThis document provides an introduction to the Symmetrix Remote Data Facility (SRDF) and itsuses in disaster recovery, high availability, and data migration applications.AudienceThis document is intended for Dell EMC customers who want an overview of SRDF and itsapplications.Related documentationInformation on the storage arrays that SRDF runs on is in the following publications:lDell EMC PowerMax Family Product GuidelDell EMC VMAX All Flash Product Guide for VMAX 250F, 450F, 850F, 950F with HYPERMAXOSlEMC VMAX3 Family Product Guide for VMAX 100K, VMAX 200K, VMAX 400K withHYPERMAX OSWhere to get helpDell EMC support, product, and licensing information can be obtained as follows:Product informationDell EMC technical support, documentation, release notes, software updates, or informationabout Dell EMC products can be obtained at https://support.emc.com (registration required)or ll-flash-family.htm.Technical supportTo open a service request through the Dell EMC Online Support (https://support.emc.com)site, you must have a valid support agreement. Contact your Dell EMC sales representativefor details about obtaining a valid support agreement or to answer any questions about youraccount.Technical supportDell EMC offers a variety of support options.lSupport by Product — Dell EMC offers consolidated, product-specific information on theWeb through the Dell EMC Online Support site.The Support by Product web pages (https://support.EMC.com/products) offer quicklinks to Documentation, White Papers, Advisories (such as frequently usedKnowledgebase articles), and Downloads, as well as more dynamic content, such aspresentations, discussion, relevant Customer Support Forum entries, and a link to DellEMC Live Chat.Dell EMC SRDF Introduction11

PREFACElDell EMC Live Chat — Open a Chat or instant message session with an Dell EMC SupportEngineer.Your commentsYour suggestions help us improve the accuracy, organization, and overall quality of thedocumentation. Send your comments and feedback to: VMAXContentFeedback@emc.com12Dell EMC SRDF Introduction

CHAPTER 1IntroductionThis chapter introduces SRDF, lists its uses, and defines SRDF's concepts.llWhat is SRDF?.14SRDF concepts. 18Dell EMC SRDF Introduction13

IntroductionWhat is SRDF?The Symmetrix Remote Data Facility (SRDF) maintains real-time (or near real-time) copies of dataon a production storage array at one or more remote storage arrays. SRDF has three primaryapplications:lDisaster recoverylHigh availabilitylData migrationThis is an introduction to SRDF, its uses, configurations, and terminology. The rest of this sectionprovides a summary of the applications for SRDF (SRDF device pairs on page 18 explains thedevice naming conventions used in the diagrams).Disaster recoveryIn disaster recovery, SRDF maintains a real-time copy of the data of one or more devices on astorage array at one or more additional arrays. This provides the means to restart host applicationsshould the main array become unavailable for any reason. Typically, each array is on a separate sitefrom all the others in the SRDF configuration.For example, this diagram shows a configuration where data is replicated to one additional array:Figure 1 Data replicated to one additional arrayOpen systems hostsProduction hostOptional remote hostRecovery pathWrite DisabledActive host pathR1Read/Write14Dell EMC SRDF IntroductionSRDF LinksR1 data copies to R2R2ReadOnly

IntroductionThe next example shows data being replicated to two additional arrays simultaneously. Thisimproves redundancy and data security:Figure 2 Data replicated to two arrays simultaneouslySite BTargetR2R11Site CTargetSite ASourceR2Disaster recovery on page 35 describes SRDF's disaster recovery facilities, and systemconfigurations in more deta

Dell EMC support, product, and licensing information can be obtained as follows: Product information Dell EMC technical support, documentation, release notes, software updates, or information about Dell EMC products can be ob