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Revision Date: June, 2013 Revision Number: MR-1WP-SDRFD. ARNO

1 SRDF Fundamentals


This course provides an overview of the Symmetrix Remote Data Facility (SRDF) solution supporting remote replication. This course provides an understanding of SRDF terminology, features, architecture and management.

2 SRDF Fundamentals


This course provides an introduction to Symmetrix Remote Data Facility (SRDF), describing its features and modes of operation.

SRDF Fundamentals 3


This module is an introduction to the remote replication business benefits; it is an overview of the SRDF family of products and provides a sample of typical use cases for this product.

SRDF Fundamentals 4


Symmetrix Remote Data Facility (SRDF) is a business solution that allows a client with Symmetrix-Based data centers to copy their data between the sites to prepare for the possibility of a disaster at their main IT site. However, there are other purposes for replicating data remotely, such as in data distribution.

What sets SRDF apart, is that the copy process between the sites is accomplished independently without the host. There are also no limits to the distance between the source and the target copies.

SRDF Fundamentals 5


The correct remote replication solution can limit exposure to planned and unplanned downtime by enabling operations at remote sites. SRDF provides an organization with efficient data replication tools to meet corporate or government standards, while still meeting Total Cost of Ownership requirements. SRDF offers data protection, and fast business restart in the event of a disaster.

SRDF Fundamentals 6


The first thing to consider when selecting an information or data protection strategy is the source of outages.

Planned downtime represented by normal housekeeping events account for approximately 85 percent of all information outages.

Next, unscheduled events account for most of the remaining 15 percent of outages.

Less than 1 percent of outages are caused by natural disasters, such as hurricanes and earthquakes, or major business events, such as mergers and acquisitions.

Planned downtime is often predictable, and manageable. So, business continuity is assured even during regular maintenance windows 85 percent of the time (or most of the time).

The other 15 percent or so can be devastating, if and when it occurs. Without preparation, an unplanned outage can severely impact the viability and profitability of a business.

Replication technologies can also be applied to scheduled events, such as occasional migrations and more frequent data re-purposing for decision support or test and development.

7 SRDF Fundamentals


The source and target are physically separated to reduce the risks associated with a disaster. Their physical distance and technology selected can affect how quickly you recover from a disruption and how much data is lost. Organizations or government regulations set requirements for how much lost data and how much time to come back online is acceptable.

Recovery point objective (RPO) is the point in time to which critical data must be restored following an interruption, before its loss severely impacts the organization.

Recovery time objective (RTO) is the amount of time that it takes to recover the data and restart business services, including critical applications central to business operations. Replication is appropriate for all types of data; however, the RPO and RTO requirements are going to affect the type of implementation.

8 SRDF Fundamentals


The key to determine which remote replication solution is best for a particular application is a thorough understanding of service levels. Specifically, there is a need to balance requirements for performance, functionality, availability, and economy against capacity needs, bandwidth requirements, and overall Total Cost of Ownership. Every solution has benefit and risk. All of these factors must be balanced in order to decide the best solution for a given problem.

In the business considerations, as shown on the left side of the slide, each of the factors listed, such as recovery time objectives, will have an impact on the requirements on the right of the scale. There is a cost attached to all factors, and these are the considerations that IT managers continuously face.

SRDF helps meet the correct business and regulatory objectives performing the following operations: disaster restart, disaster restart testing, recovery from planned outages, remote backup data center migration and data replication.

9 SRDF Fundamentals


The field-proven Symmetrix Remote Data Facility (SRDF) family is the industry’s most powerful suite of remote storage replication software available for disaster recovery and business continuity. The SRDF family offers unmatched deployment flexibility and massive scalability. The base family of products offers:

Symmetrix Remote Data Facility/Synchronous (SRDF/S), a disaster-restart solution that operates in synchronous mode and maintains a real-time (synchronous) mirrored copy of production data (R1 devices) with physically separated Symmetrix system (R2 devices).

SRDF/A operates in asynchronous mode. It is a disaster-restart solution that mirrors data from the R1 devices while maintaining a dependent-write consistent copy of the data on the R2 devices at all times. The dependent-write consistent copy of the data at the secondary site is typically only seconds behind the primary site. SRDF/A session data is transferred to the secondary Symmetrix system in cycles.

SRDF/DM is a data migration/data mobility solution that enables fast data transfer from R1 to R2 devices over extended distances. SRDF/DM operates exclusively in adaptive copy mode and it does not function in consistency mode. The additional SRDF options will be covered in more detail later in this course.

VMAX 10K supports SRDF well-proven, enterprise-wide disaster recovery solution, not a point solution for an individual application or database.

10 SRDF Fundamentals


This SRDF implementation sample is a media and entertainment industry customer with a large customer base. The primary site servers use a VMAX40K with 3 Engines with 50 100GB flash drives and 360 600GB disk drives; remotely replicated 990 KM to a target site that uses a VMAX40K with 2 Engines and 360 600GB disk drives. The approximate SRDF I/O traffic rates average about 25 MB/sec. The SRDF groups are using SRDF/A for synchronization.

SRDF Fundamentals 11


Illustrated here is a typical sample for SRDF in a VMware environment. VMware Site Recovery Manger (SRM) provides business continuity and disaster recovery. Individual datastores or an entire site can be protected.

SRDF is integrated with VMware Site Recovery Manager. SRM with SRDF automates many of the required tasks required at failover. When activated, SRM with SRDF will:

• Power down protected VMs (if they are still online)

• Suspend data replication

• Enable read/write at the recovery site

• Rescan the ESX servers at the recovery site

• Register the protected VMs at the recovery site

• Shutdown non-essential VMs at the recovery site, if required to free up resources, and

• Power on the VMs at the recovery site



This module covered an overview of the remote replication business benefits, the SRDF family of products and provided a sample of typical uses case for this product.



This module focuses on the method used to provide a remote copy of the Symmetrix data and the different types of connectivity options for its implementation.



SRDF provides comprehensive business continuity and restart capabilities for planned and unplanned outages. This online, host-independent, mirrored data solution duplicates production site data on one or more physically separate target Symmetrix systems. What makes this technology a leader in the industry is its use of track tables. Track tables maintain the differential between source and target devices; track tables have a unique capability to send only changed information at the track level. This allows SRDF to operate in several modes that are addressed later in this course.



At the primary site, a local host connects to a Symmetrix. The device containing the production data to be remotely mirrored is called the primary (R1) device, also referred to as the source device.

At the secondary site, a second host connects to the remote Symmetrix with the secondary (R2) device, also referred to as the target device, and contains the remotely mirrored data.

The R1 and R2 devices appear as a mirror to the local device. They are not a physical mirror, but an entry on the track tables. The Symmetrix system’s R1 and R2 devices communicate through SRDF links. Under normal circumstances, the R1 device presents a Read-Write (RW) status to the host that accesses the R1. The R2 device presents Write-Disabled (WD) status to its host.



The SRDF group defines the logical relationship between SRDF devices and SRDF directors on both sides of the SRDF links. It is comprised of a range of SRDF devices and SRDF directors that reside on a given Symmetrix array.

Each SRDF group communicates with the partner SRDF group that is defined in another Symmetrix array located across the SRDF links.

The SRDF mirrors that belong to these SRDF devices point to the SRDF partner devices that reside on another Symmetrix array and are configured to the partner SRDF group. There are limits to the number of SRDF groups for each Symmetrix model.



The SRDF family offers great flexibility in deployment depending on the business needs by offering fully tested, integrated and flexible hardware, software and communication options.

EMC offers native Gigabit Ethernet and Fibre capability for DMX and VMAX series systems. The Fibre Channel or Gigabit Ethernet front-end I/O module is installed and configured in the VMAX series systems.

The maximum number of SRDF supported groups and devices vary by Enginuity level; the table illustrated shows the maximum limits.

The connectivity options include:

• Asynchronous Transfer Mode (ATM)

• Internet Protocol (IP)

• Dense Wavelength Division Multiplexing (DWDM)

• Coarse Wavelength Division Multiplexing (CWDM)

• T1/E1-T3/E3, and

• Synchronous Optical Networking (SONET)

When using a Gigabit Ethernet director on the Symmetrix, there is a built-in hardware compression to maximize bandwidth utilization.



There are three types of SRDF Link configurations:

• Unidirectional

• Bidirectional, and

• Dual-directional

Unidirectional is a one-way mirror relationship.

Bidirectional is a two-way mirror relationship where data moves in both directions on the SRDF links.

Bidirectional configuration is only recommended in Campus mode due to the overhead associated with the change of direction.

Dual-directional is an extended distance solution with two unidirectional SRDF RA groups, primary and secondary, in each Symmetrix system.



Prior to Dynamic SRDF, R1 and R2 pairings were static and defined in the SymmWin SRDF configuration. Any changes to SRDF device pairing require a new configuration to be defined and loaded into the source and the target Symmetrix.

Dynamic SRDF provides the capability to change SRDF Groups and device pairings, as needed, without requiring a BIN file configuration change to be performed by EMC.

A dynamic SRDF group represents a SRDF logical link between two Symmetrix arrays. After a Dynamic SRDF group has been created, the RDF pairs can be added.

Dynamic SRDF enables the creation and deletion of SRDF pairs while the Symmetrix array is in operation. Once established, the new SRDF pairs can be synchronized and managed in the same way as configured SRDF pairs.

A requirement for Dynamic SRDF groups is ‘Switch’ connectivity, which is a SAN or GigE switch topology.



When selecting the ideal business continuance solution, the selection is determined by the distances separating the data centers, the Recovery Point Objective and Recovery Time Objective, and how well the applications tolerate network latency. Shorter distances reduce network latency, which allows using synchronous disk replication and data center mirroring. Business continuance solutions can be divided into three general categories based on the distances between the local and remote data center.

Campus solution is a limited subset of metro connectivity that uses fiber-optic cabling to transmit data over short distances using Symmetrix and SAN equipment. Typically, the distance is smaller than 66 kilometers using channel extenders or long distance fiber-optics cables.

Metropolitan Area Network provides SRDF connectivity for distances typically less than 100 kilometers, but up to 200 kilometers or more.

Extended Distance Wide Area Network provides SRDF connectivity over long distances using telecommunications networks, such as IP, SONET, or ATM.

WANs are differentiated from MANs as being asynchronous, and having limited bandwidth environments, data buffering and are compression capable.



There are several SRDF Campus implementations available that enable units to be connected locally:

Direct Fibre Channel Attach provides connection via direct cable segments attached between the two Symmetrix unit ports at a distance of up to 10 kilometers for each cable segment using single mode cable. The multimode cable is used for distances of less than 500 meters.

Switched Fibre Channel Attach provides connections between the two Symmetrix unit ports by way of Fibre Channel switch ports at a distance of up to 10 kilometers for each cable segment.

Using a 10 GigE Director in the VMAX provides native IP support for any SRDF-based product on Symmetrix systems, which is based on 10 GigE technology. This enables direct Symmetrix-to-IP network attachment. This increases the options for Symmetrix-to-Symmetrix connectivity and allows a Symmetrix system to connect to an existing Ethernet infrastructure.



The use of a Metropolitan Area Network is determined by the ability of the customer or carrier to provision ‘dark fiber’ cable, which allows the use of the entire bandwidth on that fiber.

MANs are useful for campuses with multiple data centers or Internet Service Providers (ISP) that have several sites along a fiber-optic network right-of-way or for Extended Service Pages (XSP) that need to reach multiple customers in the area. This means that the maximum bandwidth is available and the delay or latency is low and controllable.



The Extended Distance Wide Area Network solution enables units to be at trans-oceanic or trans-continental distances for all types of directors. Typically, OC3, ATM, T3, and E3 lines, or IP are offered by lease carriers.

Fibre Channel SRDF can leverage write acceleration, sometimes referred to as Fast Write, a performance enhancement feature offered by distance extension and/or switch products.



Switched SRDF enables Symmetrix systems running SRDF to be connected through any type of SAN switches. At the same time, switched SRDF enables the Symmetrix to be configured in a ‘fan out’ or ‘fan in’ configuration. The Symmetrix systems can share the bandwidth of Fibre Channel (RF Director) across fewer connections. This is possible due to the multiplexing capability of the Fibre Channel protocol. More applications can benefit from the disaster recovery with SRDF using SAN, allowing the same physical links to be shared by multiple SRDF groups in campus and extended distances.



This module covered the method used to provide a remote copy of the Symmetrix data and the different types of options available for its implementation.



This module focuses on the common SRDF modes of operation, the various connection types for each distance, and the SRDF Consistency Group feature. Also covered are the SRDF Multi-site solutions, the SRDF Migration option and the combination of SRDF and RecoverPoint features.



SRDF modes of operation are Synchronous Replication, Adaptive Copy Replication, and Asynchronous Replication.

Synchronous Replication (SRDF/S) provides real-time mirroring of data between the source Symmetrix and the target Symmetrix systems.

Adaptive Copy Replication (SRDF/DM) transfers data from the source devices to the remote devices without waiting for an acknowledgment.

Asynchronous Replication (SRDF/A) places host writes into ‘cycles’ or ‘chunks’ and then transfers an entire chunk to the target system.

These operational modes can be changed dynamically using EMC software, the operational method can be specified on a per device basis or as a device group.

Performance, level of synchronization, and I/O serialization requirements determine appropriate operational mode. The different replication modes can co-exist within the Symmetrix array.



SRDF Synchronous Mode is primarily used in SRDF campus environments. In this mode of operation, the Symmetrix maintains a real-time mirror image of the data of the remotely mirrored devices.

Data on the source (R1) devices and the target (R2) devices are always fully synchronized at the completion of an I/O sequence through a first-in, first-out queue (FIFO) model. All data movement is at the block level with synchronized mirroring.

Synchronous SRDF writes from the host to the primary and do not finish until they are acknowledged at the primary Symmetrix and the write data is resident in the secondary Symmetrix system's cache. This means that the logical device is busy at the primary host including read-following-write operations throughout the SRDF operation.



Symmetrix SRDF Adaptive copy modes facilitate data sharing and migration. These modes allow the primary and secondary devices to be more than one I/O out of synchronization. The maximum number of I/Os that the R2 can be out of synchronization is known as the maximum skew value. The default value is equal to the entire logical device. The maximum skew value for a device can be set using the SRDF monitoring and control software.

Symmetrix SRDF Adaptive Copy Disk Mode is designed for bulk data transfer. Host write tasks accumulate on the primary device as invalid tracks rather than in global memory. A background process sends the write tasks to the corresponding secondary device.

Symmetrix SRDF Adaptive Copy Write Pending Mode write-requests accumulate in cache in the primary array. A background process sends the writes to the corresponding R2 device on the other side of the SRDF links. These Adaptive Copy modes have little impact of the primary site host.



SRDF/Asynchronous (SRDF/A) is a remote mirroring solution for the Symmetrix family. Its unique architecture delivers a remote mirroring solution that has no impact on the production applications and as well as no distance limitation. This unique architecture enables significant operational savings through reduced bandwidth requirements. SRDF/A is a single solution supporting both mainframe and Open Systems.



SRDF/A uses Delta Sets to maintain a group of writes collected over a short period of time. Delta Sets enable all of the efficiencies that SRDF/A delivers. There are four types of Delta Sets to manage the data flow process.

The data flow of SRDF/A can be summarized in simple steps:

• Source-site Delta Sets include Capture and Transmit; Target-site, Receive, and Apply.

• Capture captures all incoming writes to the source devices involved in the SRDF/A group.

• Transmit transfers its contents from the source to the target system.

• Receive on the target system receives the data being transferred by the source-side Transmit Delta Set.

• The Apply cycle writes the Delta Set to the target device to create a consistent recoverable remote copy and this completes the Delta Set cycle.

A consistent recoverable copy is maintained at the remote location with each application of a Delta Set. Once the initial Delta Set cycle completes, it is repeated Delta Set after Delta Set, providing a continuous checkpoint of Delta Sets. SRDF/A provides a solution for a service-level requirements that need data on the R2 side within the range of seconds to minutes.



Each Symmetrix system requires additional cache to support the cache-resident Delta Sets. The balancing of cache to bandwidth for maximum performance is critical.

SRDF/A resiliency features enhance overall operational balance, thus helping to control Symmetrix systems.

SRDF/A Write Pacing improves the robustness of SRDF/A replication by offering the ability to throttle or slow down host write I/Os response times up to a user specified limit to maintain the required Recovery Point Objective (RPO) targets.

The Delta Set Extension Feature provides additional Delta set space in a Symmetrix disk. The disk space is allocated through software.

Transmit Idle is a SRDF link operational enhancement.



The SRDF/A write pacing feature available with Enginuity 5874 or higher helps to secure the availability of an SRDF/A session by preventing conditions that can cause cache overflow on both the R1 and R2 sides.

SRDF/A detects when the SRDF I/O service rates are lower than the host I/O rates. Then it takes corrective action to slow host I/O rates to match the SRDF I/O service rates.

The current Enginuity uses a pacing algorithm and takes a corrective action to slow or pace host I/O write rates to match the slower SRDF/A I/O service rates.

SRDF/A write pacing helps control the amount of cache used by SRDF/A. This can prevent cache from being exhausted on the R1 side of the SRDF link, thereby keeping the SRDF/A sessions alive, the options are:

• The group-level pacing option: This option requires Enginuity version 5874 or higher on both Symmetrix arrays. It is enabled for the entire SRDF/A group when reductions of transmit cycle or apply cycle rates occur.

• The device-level pacing option: This option is for SRDF/A solutions in which the SRDF/A R2 devices participate in TimeFinder copy sessions. This option requires Enginuity version 5875 or higher on both Symmetrix arrays.



SRDF/A Transmit Idle is a feature of SRDF/A that provides it with the capability of dynamically and transparently extending the Capture, Transmit, and Receive phases of the SRDF/A cycle, while masking the effects of an “all SRDF links lost” event.

Without the SRDF/A Transmit Idle feature, an “all SRDF links lost” event would normally result in the abnormal termination of SRDF/A. SRDF/A would become inactive.

The SRDF/A Transmit Idle feature has been specifically designed to prevent this event from occurring. Transmit Idle is enabled by default when dynamic SRDF groups are created. When all SRDF links are lost, SRDF/A will remain active.

The capture cycle grows in cache, eventually, if and when a cache full condition occurs, then SRDF/A will become inactive.



SRDF/A Delta Set Extension (DSE) provides a mechanism for augmenting the cache-based Delta Set buffering mechanism of SRDF/A with a disk-based buffering ability. This extended Delta Set buffering ability may allow SRDF/A to ride through larger and/or longer SRDF/A throughput imbalances than would be possible with cache-based Delta Set buffering alone.

Delta Set Extension (DSE) extends the cache space available for SRDF/A session cycles by off-loading some or all of its cycle data from cache to preconfigured disk storage, or pools, which are similar to SAVE device pools.

SRDF/A DSE Threshold sets the percentage of cache used for SRDF/A that will start off-loading cache to the disk. DSE must be enabled on both the source and target arrays.



Data compression of SRDF data is provided as part of the SRDF Enginuity software for VMAX-20K. It is available to SRDF/S, SRDF/A, and SRDF/DM over Fibre Channel and GigE directors with Enginuity 5874 and higher.

If software compression is enabled, Enginuity compresses data before sending it across the SRDF links, but both sides of the SRDF links must support software compression.

Hardware compression is available for GigE SRDF traffic on VMAX 20K or VMAX 40K arrays, whereas hardware compression for SRDF traffic over Fibre Channel is available for VMAX 40K only.

Both Enginuity software and hardware compression can be activated simultaneously for SRDF traffic over GigE and Fibre Channel. Data is first compressed by software and then further compressed by the Symmetrix hardware.

The benefit of SRDF compression reduces inter-site network costs associated with SRDF replication, giving additional network bandwidth to other applications.



Dependent write is a write I/O operation that depends on a previous I/O write to be completed before its execution. All logging database management systems use this concept to maintain integrity. This is required for protection against local power outages, loss of local channel connectivity, or storage devices. There is a logical dependency between the I/Os written to database management systems, certain applications and operating systems.



SRDF Consistency Groups allow customers to define logical device groups, which can be associated with given workloads. These groups of SRDF logical devices are automatically suspended, in case of SRDF communications failures.

This feature includes the ability to do an ‘explicit trip’ of the affected consistency group. An explicit trip means that SRDF transfers to the R2 side are simultaneously stopped, leaving the R2 devices in a ‘consistent’ state as of the last transfer of information. As such, the R2 devices can be made restartable in a test or recovery procedure.

This Symmetrix 2 times 2 configuration illustrates how one pair of the SRDF links become inoperable between the sites configured in a Consistency Group. The host receives the error message and initiates the command to perform a suspend operation across all SRDF R1 devices to the R2 devices in the Consistency Group.



SRDF/AR is an automated remote replication solution that uses both SRDF and TimeFinder to provide a periodic asynchronous remote replication of a restartable data image for mainframe, UNIX, and Windows operating system environments. It is offered with SRDF/AR Single Hop and SRDF/AR Multi-Hop.

SRDF/AR Single Hop is composed of a source or a production site, and a target or a restart site. The attached hosts can be mainframe, UNIX, and/or Windows. All operations are managed by EMC software.

The target site shows that the R2s are split from their BCVs. The standard devices at the source site represent the dependent write-consistent copy.

The standard devices show that logical consistency is maintained by utilizing TimeFinder Consistent Split.



In a multi-hop configuration, there is a synchronous propagation from the source site (Site A) to the bunker site (Site B), and adaptive copy propagation from the bunker site to the target site (Site C).

The function of the bunker site is to transform synchronous propagation to an adaptive copy propagation of dependent write-consistent copies. The distance from the bunker site to the target site is usually a long distance and uses the adaptive copy mode. The propagation between the bunker site and the target site is accomplished via EMC software and managed by the user.

This solution addresses the customer’s requirement to have a consistent mirror device to provide for disaster restart at the multi-hop site if necessary. It also provides the ability to have data currency at the SRDF Multi-Hop site.



Cascaded SRDF uses a dual role SRDF R1-R2 device referred to as an SRDF R21 device on the secondary site, which is a real device and acts both as an R2 to the primary site and an R1 to the tertiary site.

The major benefit provided with a ‘cascading’ configuration is its inherent capability to continue replicating from the secondary site to the tertiary site in the event that the primary site goes down.

This enables better RPO and, most likely, better RTO at the tertiary site with zero data loss achievable up to the point of the primary site failure, or disaster event.



Symmetrix Remote Data Facility Extended Distance Protection is a new three-site ‘No Data Loss’ extended distance disaster protection solution.

SRDF/EDP uses the basic cascaded SRDF configuration. The device ‘R21’ is a cache only device. There are only two full copies of data, one at Site A and one at Site C. There is no disk copy of data at Site B.



SRDF for VMAX supports remote replication to Symmetrix VMAX along with three-site and Star configurations.

Cascaded SRDF/STAR (top left Illustration) allows a synchronous R2 target to also act as a source for SRDF/A. The long distance site in cascaded RDF uses this source to receive its data. In the event of a failure of the workload site, the synchronous target has up to date data. The asynchronous target data is not more than two SRDF/A cycles behind the source site data.

Concurrent SRDF/Star (bottom left illustration) enables concurrent SRDF/S and SRDF/A operations from the same source devices. The primary business benefit of Star is that in the event of a workload site outage, it is possible to undertake a differential resynchronization between the two remaining sites, followed by the resumption of production at either site.

SRDF/SQAR, or Symmetrix Quadrilateral Asynchronous Replication (right illustration), is a four-site implementation of SRDF/S and SRDF/A that enables differential resynchronization between sites along the perimeter of a 'square' multi-site SRDF topology. Its principle objective is to meet the requirement for a multi-region high availability and disaster restart solution.



SRDF can be used for migrations from older to newer Symmetrix systems with Enginuity versions 5875 and higher. SRDF provides thick-to-thin migration solutions that use concurrent SRDF.

A temporary concurrent SRDF topology is created only for the migration process that enables the user to non-disruptively migrate data between the Symmetrix systems along one concurrent SRDF branch, while keeping remote mirroring for protection along the other concurrent SRDF branch. Once the migration process completes, the concurrent SRDF topology is removed, thereby resulting in a two-site SRDF topology. EMC host-based SRDF control software is used to automate the migration process.



SRDF and RecoverPoint can be used to protect the same data, combining the gold standard for remote replication with unique local Continuous Data Protection, or CDP. RecoverPoint provides Digital Video Recording (DVR), like recovery to any point in time.

Typical usage for this solution would be a customer that currently has a database application setup with synchronous SRDF for compliance reasons. SRDF can protect against site failure, but not against logical corruption of the database. By adding CDP to the R1 device, the customer gets ‘DVR,’ like recovery with minimal or zero RPO, in case of data corruption. In the case of logical corruption, the restore from the local RP copy to the R1 device will automatically be propagated to the R2 device, and will greatly reduce recovery time.



EMC has the right solution for each particular requirement. If the customer cannot tolerate any data exposure, then EMC has the industry leading solution for synchronous mirroring with SRDF.

However, as with any synchronous solution, there are characteristics that must be understood. Distance is limited by application time-outs and speed-of-light issues. Bandwidth must be sized for peak workload at all times. The table on this slide shows the comparison between the different options for each particular application.



This module covered the common SRDF modes of operation, the various connection types for each distance, and the SRDF Consistency Group feature. Also covered, were SRDF Multi-site solutions, the SRDF Migration option and the combination of SRDF and RecoverPoint features.



This module focuses on the various SRDF management tools, and the most common SRDF recovery operations.



Many possibilities exist to manage the SRDF environment for each particular business objective; only a few will be mentioned in this section.

The EMC® Solutions Enabler is a specialized library consisting of commands that can be invoked on the command line, or within scripts. These commands can be used to monitor device configuration and status, and perform control operations on the SRDF features. Other open system software packages will be discussed later.

For Mainframe, SRDF Host Component monitors SRDF status and controls SRDF processes through the use of commands executed from a host.

EMC z/OS Storage Manager (EzSM) is designed to report on Symmetrix® mainframe storage. EzSM provides mainframe operation’s staff with a z/OS-oriented view of storage through an easy-to-use ISPF interface.

Geographically Dispersed Disaster Restart (GDDR) automates disaster restart of applications and systems in mainframe environments in the event of a planned or an unplanned regional outage.



Unisphere for VMAX is EMC's new management console for the Symmetrix VMAX Family. Unisphere for VMAX offers navigation and streamlined operations to simplify and reduce the time required to manage your data center.

Unisphere for VMAX provides a user interface for the configuration and management of Symmetrix arrays and can be used to operate and monitor SRDF remote mirroring functions. Additionally, Unisphere for VMAX provides health indicators for SRDF/A cache usage, cycle time, and throughput at user-configurable polling intervals.

Unisphere for VMAX is contextual and simple to navigate, with Unisphere; users can easily and rapidly manage and monitor all Symmetrix VMAX SRDF features.



EMC ProSphere provides end-to-end views across your virtual and physical environments. From virtual guest down through storage, with just two clicks of the mouse, we can search on a host and display end-to-end topology and SRDF relationship views. EMC ProSphere provides views to understand SRDF feature usage and trends.

EMC ProSphere can monitor alerts across the total Symmetrix local and remote environments and drill down to quickly understand their impact.



EMC’s Watch4net software suite is a carrier-class for network providers; performance reporting that shows real-time, historical, and projected visibility into the performance of the Symmetrix local and remote topology. This software allows collecting and aggregating performance data from various sources, including SRDF networks, into a single repository, as illustrated on this slide. With proactive performance management, Watch4net provides proactive alerting, including situations to watch SRDF application network traffic.



The EMC software management tools will assist in the various recovery operations. SRDF recovery operations fall into these categories:

Planned failover, which is used for testing or maintenance - a planned failover is a controlled failover operation to test the robustness of the disaster restart solution. Production is temporarily moved to the secondary site during a planned failover.

Unplanned Failover – the production processing is moved from the primary to the secondary site due to an unexpected failure of the production host at the primary site, the primary Symmetrix system, or both.

Failback - once the primary site and/or the production host are restored or repaired, the production processing is resumed at the primary site.

Split – sometimes referred to as Concurrent Operations, places the Symmetrix units in a state for concurrent access, and suspends the link between source (R1) and target (R2) devices. Read and write operations on both source and target devices are enabled.

Establish- Saves source data, resumes normal SRDF operations, preserves data on the source (R1) devices and discards changes to the target (R2) devices.

Restore- Resumes SRDF operations, preserves data on the target (R2) devices and discards changes to the source (R1) devices



The Failover process makes a copy of the data on the target Symmetrix devices available to attached hosts. It could be utilized during a disaster scenario, such as a host channel, Symmetrix, or site failure. It could also be used during maintenance activities.

The Failover process causes the target devices to take over read/write operations for source devices. This operation will halt all I/O activity and write-disable the source devices. This operation is typically performed when the user needs to transfer production from the source to the target devices.



The Failback process or returning control to the local host resumes I/O operations with the source devices after a period of performing I/O operations with the target devices. This operation will halt all I/O activity and write-disable the target devices. This operation is typically performed when returning to a normal SRDF operation after a failover.



The split process stops remote mirroring between the source device and the target device. The target device is made available for local host operations.

On a split operation, the link is suspended between the source and the target devices, then read and write operations are enabled on both R1 and R2 devices.



In this scenario, a user was upgrading the database software and had split a pair of SRDF devices to upgrade/test the new code on the target. The database upgrade has failed. The user has decided to keep the source side, or the non-upgraded side, as the production environment until the user confers with the database company, tries the upgrade, and tests when the issues are sorted out.

The user copies the source data to the target side. In open systems, this process is referred to as an ‘Establish’.

In the Establish, the connection is restored and changed tracks on the source side are updated to the target. Tracks changed on the target are overwritten with the information from the source side, even if the source tracks were never changed. Tracks left untouched on both sides are not re-synched. The incremental operation is achieved by comparing the track table for the source with the table for the target.



The full restore operation differs from the establish operations in that the entire contents of the target (R2) device is copied to the source (R1) device. After the restore control operation is completed, the pairs are fully synchronized.



SRDF enables R1/R2 swapping with the R1s becoming R2s, and R2s becoming R1s. This results in the reversal of the data mirroring flow and facilitates continual disaster recovery readiness during workload migrations. This also eliminates resynchronization, as remote mirroring operations occur between the swapped sites.

This allows for continued servicing of the application and data from the remote site as long as the source Symmetrix and SRDF inter-site links remain online in the event that the primary site and host environment go offline.



This module covered the various SRDF management tools, and the most common SRDF recovery operations.



This course covered an introduction to components of SRDF, the benefits of remote replication, SRDF connections and configurations of SRDF. Also covered, were the SRDF modes of operation, management software and recovery operations.

This concludes the training. Proceed to the course assessment on the next slide.


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