m02res01

Copyright 2005 EMC Corporation. Do not Copy - All Rights Reserved.

SRDF Overview Mod 2

2005 EMC Corporation. All rights reserved.

Symmetrix Business Continuity SRDF SolutionsSymmetrix Business Continuity SRDF Solutions

Module II - SRDF/S (Synchronous)

These materials may not be copied without EMC's written consent.

EMC 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. EMC CORPORATION MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WITH RESPECT TO THE INFORMATION IN THIS PUBLICATION, AND SPECIFICALLYDISCLAIMS IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR APARTICULAR PURPOSE.

Use, copying, and distribution of any EMC software described in this publication requires an applicable software license.

EMC and SRDF are trademarks of EMC Corporation.

All other trademarks used herein are the property of their respective owners


SRDF Overview Mod 2

2005 EMC Corporation. All rights reserved. Mod 2 Page 2

SRDF Introduction1

SRDF/A (Asynchronous)4

SRDF/AR (Automated Replication)5

SRDF (Consistency Technology)6

SRDF Labs 1-7

SRDF Operations

SRDF/S (Synchronous)

MOdule Name

Second Pass after T3 06-Jun-2005

First Pass 28-Mar-2005

Revision NumberActivity - Notes

***

BCR_Mod2_V21.Ppt

BCR_Mod2_V12a.Ppt

BCR_Mod2_V10a.Ppt

File Name

28-Mar-20051.0a

Name Change26-Jul-20051.2a

12-Sep-20052.1a

Module #

2

3

7

DateRev#

Revision HistorySymmetrix Business Continuity SRDF Solutions

Module - II SRDF/S (Synchronous)

Copyright 2005 EMC Corporation. All rights reserved.

These materials may not be copied without EMC's written consent.

EMC 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. EMC CORPORATION MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WITH RESPECT TO THE INFORMATION IN THIS PUBLICATION, AND SPECIFICALLYDISCLAIMS IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR APARTICULAR PURPOSE.

Use, copying, and distribution of any EMC software described in this publication requires an applicable software license.

EMC, and SRDF are trademarks of EMC Corporation.

All other trademarks used herein are the property of their respective owners.


SRDF Overview Mod 2


Module Objectives SRDF/S SynchronousSymmetrix Business Continuity SRDF

SolutionsAt the completion of this module, the student will be able to

Describe SRDF solutions Describe EMC SRDF functionality and its uses Describe SRDF Link configurations Describe the concept of SRDF Group Describe SRDF swap List the characteristics of Concurrent SRDF List the characteristics of Dynamic SRDF

The above objectives are covered in this module

Program Symmetrix Business Continuity SRDF Solutions.

Module Name SRDF/S Synchronous .

Module Number - II


SRDF Overview Mod 2


Symmetrix Remote Data Facility (SRDF)

y Facility for maintaining real-time or near-real-time physically separate mirrors of selected volumes

y Uses no host CPU resources Mirroring done at the storage

level

y Operating system independent Open Systems Mainframe

R1 R2

SRDF

Symmetrix Remote Data Facility (SRDF) is a Symmetrix system based business continuance, disaster recovery, restart, and data mobility solution. In the simplest terms, SRDF is a configuration of multiple Symmetrix units that maintains real time copies of logical volume data in more than one location. The Symmetrix units can be in the same room, in different buildings within the same campus, or hundreds and even thousands of miles apart.


SRDF Overview Mod 2


z Symmetrix Logical Volume types: SRDF Source or R1 Volumes - Primary Volume with R/W access to

local host SRDF Target or R2 Volumes - Backup Volume used for DS or DR

Applications

z The attached host is unaware of SRDF protection

SRDF Source and Target Volumes

WDRW

M1 M4M3 M4M2 M3M1M2

TargetSource

This shows the representation of the mirror positions when both the Source and the Target SRDF Logical Volumes have local protection (RAID-1) also.

In this diagram, the Target-R2 volume is also represented with 4 mirror positions and has local protection implemented. Three of the mirror positions are used. The first two mirror positions represent local mirrors and the third mirror is occupied by SRDF. If a BCV is established with the R2 volume, then it will occupy the next available mirror position.

Under normal circumstances, the R1 volume presents a Read-Write (RW) status to the host which access it, and the R2 presents Write-Disabled (WD) to its host.


SRDF Overview Mod 2


Remote Link Director (RLD)

RemoteLink

Director

RemoteLink

Director

TargetRemoteLink

Director

RemoteLink

Director

Source

A Remote Link Director is a hardware that provides communication and data path between the local and remote Symmetrix units. The Symmetrix can be configured with the following RLDs:

- Fibre Channel directors (RF)

- ESCON directors (RA)

- Multiprotocol Channel Directors (MPCD) available with these channel connections:

FICON

iSCSI for host

GigE (RE) for SRDF


SRDF Overview Mod 2


SRDF Groups

RemoteLink

Director

RemoteLink

Director

RemoteLink

Director

RemoteLink

Director

R1R1

R1 R1 R2R2R2 R2

R2R2R2

R1R1

R1

RDF Group 1RDF Group 1

RDF Group 2RDF Group 2

RDF Group 1,2,3.

RDF Group 1,2,3.

An SRDF group, also known as RDF group or RA group, logically defines relationships between Symmetrix systems. An SRDF group is a set of SRDF director port connections configured to communicate with a another set of SRDF director ports in another Symmetrix system. Logical volumes (devices) are assigned to SRDF groups.

Many SRDF groups can share a physical link between the Remote Link Directors. There are two ways to create an RDF group, static and dynamic. Both shares the same features and functionality. The difference between the two types is how they are created. Static RDF groups are created during the Symmetrix configuration; almost always by EMC personnel. Dynamic RDF groups are created and deleted by users through a set of Symmetrix command line interface (SYMCLI) commands. The Symmetrix DMX supports up to 64 total RDF groups.


SRDF Overview Mod 2


Uni-Directional Symmetrix ASource

Symmetrix BTarget

Bi-Directional Symmetrix A Symmetrix BSource TargetTarget Source

Dual Configuration

Symmetrix A Symmetrix B

Source TargetSource Target

Target SourceTarget Source

SRDF Link Configuration

RA Group

RA Group

RA Group

RAGroup 1

RAGroup 1

RAGroup 2

RAGroup 2

RAGroup

SRDF offers three types of link configurations between source (local) and target (remote) Symmetrix systems: Uni-Directional, Bidirectional and Dual Configuration.

SRDF Unidirectional Link Configuration

If all primary (source or R1) volumes reside in one Symmetrix system and all secondary (target or R2) volumes reside in another Symmetrix

system, write operations move in one direction, from primary to secondary. Data moves in the same direction over every link in the SRDF group.

SRDF Bidirectional Link Configuration

If an SRDF group contains both primary and secondary volumes, write operations move data in both directions over the SRDF links for

that group.

SRDF Dual-Directional Link Configuration

With a dual-directional configuration, multiple SRDF groups are used; some groups send data in one direction, while other groups send data in the opposite

direction.


SRDF Overview Mod 2


Fibre Link Point-to-point Campusy Point-to-point Campus.

Simplest configuration Can be ESCON or Fibre Channel

based Best suited to environments

where primary and secondary sites are relatively close

SRDF/FC setups can also include switches where primary and secondary sites are more than 3 Km apart

Mainframe, Open Systems

SRDF

SourceSymmetrix

SCSIFC-ALFC-SWiSCSI

orESCONFICON

TargetSymmetrix

A Point-to-point Campus Mode has two Symmetrix connected by a fibre optic link less than 3 kilometers long. In this configuration, one Symmetrix might be located in one building, and the other in a separate building. While physically close, the configuration allows for separate power and other operating security considerations.


SRDF Overview Mod 2


Fibre Link Switched Campus

y Switched campus Slightly more complicated than

simple point-to-point Must be built on a Fibre Channel

infrastructure Use of FC switches mandatory Switch latency is typically

negligible Useful in environments requiring

consolidation of multiple primary storage frames into fewer secondary frames

TargetSymmetrix

Mainframe, Open Systems

SourceSymmetrix

SRDF/FC

SourceSymmetrix

Connectrix

SRDF/FC

SCSIFC-ALFC-SWiSCSI

orESCONFICON

The SRDF campus solution enables source and target units to be up to 60 kilometers apart. The campus solution uses single-mode private or leased common carrier IBM ESCON fiber cable, link extenders, and/or dynamic switches. Campus solutions require link extenders or repeaters.


SRDF Overview Mod 2


Fibre Link Extended Distancey Extended Distance

Good for distances up to 200 Km (ESCON) or 120 Km (FC) If using FC, must also include switches on both sides of DWDM link to

cater for increased buffer credit requirement Impact of DWDM link length on propagation delay (1 ms for every 200

Km of link length) must be considered

EMC Connectrix

EMC Symmetrix

EMC Symmetrix

EMC Connectrix

DWDMs (Band 1)

DWDMs (Band 2)

FC ISL (MM or SM)

FC links (MM or SM)

FC ISL (MM or SM)

FC links (MM or SM)

NDSF Fibre (50Km ring or

200Km point to point)

Using the Fibre Channel protocol allows SRDF networks to enjoy the benefits of optical networks up to a distance of up to 200 kilometers using DWDM technology. Fibre Channel based SRDF configurations must go through a switch first before connecting to the multiplexor.

With ESCON-based SRDF, users can connect directly to the dense wavelength division multiplexers.

Being able to run either ESCON and /or Fibre Channel over a DWDM network shows the flexibility of this protocol independent technology.

Multiplexing provides the opportunity to condense multiple signals down a common optic link. Using this technology, multiple Symmetrix(s) can move SRDF data through a single multiplexer to a multiple Symmetrix(s) at a remote location(s).

Distances have currently been qualified up to 200Km; however, refer to the EMC Support Matrix for the latest multiplexers and distances qualified.


SRDF Overview Mod 2


Typical SRDF Extended Distance Infrastructure

Open Systems

SRDF/ESCONor

SRDF/FC

Sour

ce

Symm

etrix

MainframeESCONFICON

SCSIiSCSIFC-ALFC-SW

Chan

nel

Exten

der

Access Point

Access Point

Telco Network Ch

anne

l

Exten

der

Targ

etSy

mmetr

ix

Proprietarychannel extension

protocol or IP

SRDF/ESCONor

SRDF/FC

The SRDF extended distance solution uses leased T1, E1, T3, E3, or ATM high-speed data lines instead of ESCON fiber cables. The maximum distance between source and target units is determined by the carrier's limitations. The extended distance solution is used most often for distances over 60 kilometers, but it can be used for distances under 60 kilometers if private or leased ESCON fiber cable is too expensive or not available.


SRDF Overview Mod 2


Native GigE and iSCSI support

Open Systems

SRDF/IP

SourceSymmetrix

MainframeESCONFICON

SCSIiSCSIFC-ALFC-SW

TargetSymmetrix

RouterRouter

IP-BasedNetwork

Native IP support for any SRDF based product on Symmetrix systems is based on GigE technology that enables direct Symmetrix system-to-IP-network attachment. This increases the distance for Symmetrix system to Symmetrix system connectivity and allows a Symmetrix system to connect to existing Ethernet infrastructure and directly access high-speed data transmission conduits via IP.


SRDF Overview Mod 2


SRDF Connectivity

y SRDF over ESCON Direct Fiber, Multimode ~ 3 Km/cable segment Fiber Repeaters/Converters ~ 20 - 30 Km/cable segment, maximum

of three repeaters DWDM, WDM (MAN) ~ 200 Km LAN/WAN - T1/E1, T3/E3, ATM, IP ~ Unlimited

y SRDF over Fibre Channel Direct Fiber, Multi mode ~ 500 m/cable segment Direct Fiber, Single mode ~ 10 Km/cable segment FC-Switch to FC-Switch ~ 20 Km total, maximum of three switches DWDM (MAN) ~ 200 Km LAN/WAN IP ~ Unlimited

Please refer to the EMC Support Matrix for the most up to date information on qualified hardware, data transfer protocol, and distance limitations.


SRDF Overview Mod 2


SRDF - Modes of Operationsy Primary and Secondary Modes

Two Primary SRDF Modes Synchronous Semi-synchronous

Secondary SRDF Mode Adaptive Copy

Write Pending Disk Mode

Operational Modes are set on Symmetrix Logical Volume level Using GUI or CLI and can be changed dynamically

y SRDF/A - Asynchronousy Domino Mode

Six operational modes are possible on SRDF operations; Synchronous mode, Semi-Synchronous mode, Adaptive Copy-Write Pending mode, Adaptive Copy-Disk Copy mode, Domino, and Asynchronous mode.

These operational modes are selectable based on many requirements such as RPO, bandwidth, and performance. One of the two primary SRDF modes of operations is set at the source (R1) volume during Symmetrix configuration. All source (R1) volumes are configured for either the Synchronous or Semi-Synchronous mode. These two modes are considered to be pre-determined SRDF modes, which may be altered using SymCli. Adaptive copy is the secondary mode that facilitates data sharing and migration. Asynchronous mode continually collects and sends data to the remote Symmetrix. Asynchronous mode must be set for the entire RA group. Users can set SRDF to function in a secondary or Asynchronous mode. SRDF will revert to the pre-determined primary mode if it cannot maintain the criteria to remain in the secondary mode. However, this is not true with Domino mode where both local and target SRDF volume will be unavailable to the host should the target host become unavailable for any reasons.


SRDF Overview Mod 2


Source Target

SRDF links

Write I/O received from host/server at the sourceThe I/O is transmitted to the target

An acknowledgment is provided by target back to the sourceThe I/O is serviced to the host

SRDF Modes of OperationSynchronous Mode

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

Data on the source (R1) volumes and the target (R2) volumes are always fully synchronized at the completion of an I/O sequence.

The sequence of operations is:y A write is received from the host/server at the source.y The write is transmitted to the target.y An acknowledgment is provided by the target back to the source.y The write is acknowledged to the Host.

If step 3 never happens, the source SRDF will service the I/O after a pre-determined timeout to keep the production machine running.


SRDF Overview Mod 2


SRDF Modes of OperationSemi-Synchronous Mode

Source Target

SRDF links

Write I/O received from host/server at the sourceThe I/O is serviced to the host

The I/O is transmitted to target

An acknowledgment provided by target back to source

SRDF Semi-Synchronous Mode is used primarily in extended distance environments. semi-synchronous mode allows the primary and secondary volumes to be out of

synchronization by one write I/O operation. Data must be successfully stored in the Symmetrix system containing the primary volume before an acknowledgement is sent to the local host.

Semi-synchronous mode will not allow the next write operation to a primary device until a positive acknowledgement is received from

the target Symmetrix system that the first write operation was received in the target Symmetrix global memory. However, any number of read operations can be performed to the primary device

while awaiting acknowledgement of the first write operation. Semi-synchronous mode writes data to the primary device in the source Symmetrix system, completes the I/O, and then synchronizes

the data with the secondary device in the target Symmetrix.

The sequence of operations is:y An I/O write is received from the host/server at the source.y The I/O is serviced to the host/server.y The I/O is transmitted to the cache of the target.y An acknowledgment is provided by the target back to the source.


SRDF Overview Mod 2


SRDF Modes of OperationAdaptive Copy Mode

Source Target

SRDF links

Write I/O received from host/server at the source

The I/O is serviced to the host

I/O accumulates in/on:- Symmetrix cache Write Pending Mode- R1 volumes Disk Mode

I/O is transmitted to the targetAn acknowledgment is provided by target back to the source

SRDF Adaptive Copy Mode is used primarily for data migrations and data center moves. This operational mode is not recommended for use when mirroring for disaster recovery/restart purposes unless used with TimeFinder.

SRDF Adaptive Copy Mode allows the source (R1) volumes and target (R2) volumes to be a out of synchronization by a number of I/Os that users can define, skew value. There are two types of adaptive copy: Write Pending Mode and Disk Mode. Adaptive Copy data movement is handled at the track level. The target data is only usable after a full synchronization.

The sequence of operations is:y An I/O write is received from the host/server at the source.y I/O is accumulating.y I/O is serviced.y The I/O is transmitted to the target.y An acknowledgment is provided by the target back to the source.

In Write Pending Mode, the unit of transfer across the SRDF link is the updated blocks rather than an entire track, resulting in more efficient use of SRDF link bandwidth. Data is read from global memory than from disk, thus improving overall system performance. However, the global memory is temporarily consumed by the data until it is transferred across the link.

In Disk Mode, while less global memory is consumed it is typically slower to read data from disk than from global memory, additionally, more bandwidth is used

b h i f f i h i k I ddi i b i i l d d


SRDF Overview Mod 2


SRDF Modes of OperationAsynchronous

Source Target

SRDF links

Write I/O received from host/server at the sourceThe I/O accumulates in Source Symmetrix cacheThe I/O is serviced to the hostThe I/O is continually transmitted to the target

The I/O accumulates in Target Symmetrix cache

SRDF/A provides a long-distance replication solution with minimal impact on performance. This protection level is intended for customers requiring minimal host application impact, who need to maintain a restartable copy of data at the target site at all time.

SRDF/A continually process Write I/Os in batches. The interval between batches is referred to as a cycle.

The sequence of operations is:y An I/O write is received from the host/server into the cache of the source.y I/O is accumulating y I/O is servicedy The I/O is transmitted to the target.


SRDF Overview Mod 2


SRDF Modes of OperationDomino Mode with SRDF/Synchronous

Source Target

SRDF links

Write I/O received from host/server at the sourceThe I/O fails to transmit to the target

Both Source and Target become unavailable

Domino Mode is used in conjunction with other SRDF modes except SRDF/A. It effectively stop all write operations to both source and target volumes if target volume become unavailable, or if all SRDF links become unavailable. User will need to manually re-enable the source volumes. While such a shutdown temporarily halts production processing, domino modes can prevent data integrity exposure that causes the inconsistent image on the target volume.


SRDF Overview Mod 2


- Synchronous ModeSource = Target

- Semi Synchronous ModeSource TargetAt most, Source is 1 I/O ahead of Target, per volume.

- Adaptive CopySource TargetSource may be up to 65535 tracks per volume ahead of Target.Skew value set per logical volume.

- AsynchronousSRDF/A Source is minutes ahead of Target.SRDF/AR Source is hours ahead of Target .

SRDF Level of Synchronization

SRDF offers considerable flexibility for various levels of synchronization. To determine the level of synchronization, one must understand the required Recovery Point Objective. This is the amount of data that can be lost in the event of a site outage. There are other factors like distance, bandwidth, and response time latency that must be considered before determining a synchronization level.


SRDF Overview Mod 2


SRDF Serializationy Writes to the Target volumes must happen in the same order

as they are written to the Source in order to have an instance in time consistent and recoverable copy

y In Synchronous, Semi-synchronous and Asynchronous modes, writes are sent to the remote Symmetrix in the order received. If the remote Symmetrix is not accessible, writes are

accumulated as invalid tracks When the remote Symmetrix becomes available, invalid

tracks are sent without regard to serialization

y Serialization is not maintained in Adaptive Copy mode Typically used for data migrations.

Serialization maintains the order in which writes are received at the remote (target) Symmetrix. SRDF serialization must be maintained in order to have a recoverable/restartable copy of data at a target site. Through serialization, write fidelity is guaranteed. In normal operations, SRDF maintains order writes with Synchronous, Semi-synchronous, and Asynchronous modes. But when the link becomes unavailable for any reason, writes accumulate as invalid tracks which the application continues to function on the host. When the link is restored, the Adaptive Copy mode is used to propagate changes across the link. This introduces risk, since serialization is not maintained with Adaptive Copy.


SRDF Overview Mod 2


T1 T2 T3 T432k 32k 32k 32k

T5 T6 T7 T832k 32k 32k 32k

T1 T3 T432k 32k 32k 32k

T5 T6 T732k 32k 32k 32k

SRDF / DM

Source R1 Target R2

Tracks

Adaptive Copy Disk Mode

The slide shows Adaptive Copy Disk Mode during in operation. SRDF does not guarantee serialization of the tracks being transferred in this mode. In this example, track2 and track 8 may not be present on the target volume at the time of disaster rendering the target volume useless. Therefore, the target volume will not serve as a disaster protection mechanism. The consistency of the target volume is not maintained during the replication process in Adaptive Copy Write Pending or Disk Mode. The target will be consistent only after the replication has completed.


SRDF Overview Mod 2


Dynamic SRDFy Enables user to dynamically define relationships between R1 and

R2 volumes

y Provides flexibility for user to tailor SRDF configuration to their changing application requirements

001

STD

001

R1

054

R2

054

STD

001

R1

054

R2

001

STD

054

STD

Connectrix(s)

Create pair

Establish

Delete pair

Prior to Dynamic SRDF, the R1 and R2 pairings were static and defined in the configuration file (BIN File) on the Symmetrix. Any changes to SRDF device pairing required a new BIN file to be defined and loaded into the Source and Target Symmetrix.

Dynamic SRDF available with 5x68 Enginuity code will provide the capability to change device pairings on the fly without requiring a BIN file configuration change to be performed by an EMC Customer Engineers.


SRDF Overview Mod 2


R1/R2 Swap

001

R1

001

R2

054

R2

054

R1Connectrix(s)

An R1/R2 personality swap (or R1/R2 swap) refers to when the RDF personality of the RDF device designations of a specified device group are swapped so that source R1 device(s) become target R2

device(s) and target R2 device(s) become source R1 device(s). Dynamic RDF swaps are available with Enginuityversion 5567 or later. To perform an R1/R2 swap, you must have an SRDF license with Symmetrix 5567 microcode or higher and Dynamic RDF must be enabled in your Symmetrix configuration.

Sample scenarios for R1/R2 Swap

- Symmetrix Load Balancing

In todays rapidly changing computing environments, it is often necessary to deploy applications and storage on a different Symmetrix without having to give up disaster protection. R1/R2 swap can enable this redeployment with minimal disruption, while offering the benefit of load balancing across two Symmetrix storage arrays.

- Primary Data Center Relocation

Sometimes a primary data center needs to be relocated to accommodate business practices. For example, several financial institutions in New York City routinely relocate their primary data center across the Hudson River to New Jersey as part of their disaster drills. R1/R2 swaps allow these customers to run their primary applications in their New Jersey data centers. The Manhattan data centers now act as the disaster protection site.

- Post-Failover Temporary Protection Measure

If the hosts on the source side are down for maintenance, R1/R2 swap permits the relocation of production computing to the target site without giving up the security of remote data protection. When all problems have been solved on the local Symmetrix, you will have to failover again and swap the personality of the devices to go back to the original configuration.


SRDF Overview Mod 2


Concurrent SRDF One R1 can be paired with two R2 devices, concurrently Remote BCVs can be associated with only one of the R2 mirrors

Source

M1 M4M2 M3

Target B

M1 M4M2 M3

Target A

M1 M4M2 M3

Connectrix(s)

Concurrent SRDF allows two remote SRDF mirrors of a single R1 device, e.g. use one remote copy for disaster recovery, and another for decision support or backup.

Each Remote Link Director is assigned to an RA Group. With ESCON, only one RA group per RLD is allowed, but Fibre Channel SRDF RA Groups can be defined to the same RLD.

Any mixture of SRDF modes is allowed, except for Sync and Semi-sync configuration and Asyncand Async configuration.

A write IO from the host at the primary device side cannot be returned as completed until both remote Symmetrix signal the local Symmetrix that the SRDF IO is in cache at the remote side.

1 Sync and 1 Adaptive Copy remote mirror:

The SRDF IO from the secondary device operating in Synchronous mode must present ending status to the sending Symmetrix before a second host IO can be accepted. The host I/O does not wait for the secondary device operating in Adaptive Copy mode.


SRDF Overview Mod 2


Concurrent SRDF

One R1 can be paired with two R2 devices, one in each Symmetrix, concurrently.

All combinations of Primary/Secondary modes for the R1-R2 pairs are allowed - except one pair in Sync and the other in semi-sync, both cannot be Async.

Cannot restore from both R2 mirrors to the R1 simultaneously. SRDF swap is not allowed - for example if the R1 is changed

to an R2 one will be left with R2->R1, R2->R2@#!

Remote BCVs can be associated with only one of the R2 mirrors.

A BCV can only be established with one of the Target volumes, not both. In case that the source is locally protected, the BCV device then cannot be established with its source, because all four(4) mirror positions will be occupied

2 Synchronous remote mirrors : y A write IO from the host at the primary device side cannot be returned as completed until both

remote Symmetrix signal the local Symmetrix that the SRDF IO is in cache at the remote side.

1 Sync and 1 Adaptive Copy remote mirror:y The SRDF IO from the secondary device operating in Synchronous mode must present ending

status to the sending Symmetrix before a second host IO can be accepted. The host I/O does not wait for the secondary device operating in Adaptive Copy mode.

The same general principle applies when both remote mirrors are operating in Semi-Sync mode.


SRDF Overview Mod 2


Module Summary

Key points covered in this Module :

y Presented an overview of SRDF solutions. y Presented SRDF functionality and its uses.y Described SRDF Link configurations. y Described the concept of SRDF Groupsy Described SRDF swap functionality.y Listed the characteristics of Concurrent SRDF.y Listed the characteristics of Dynamic SRDF.

The following Module Summary / Key Point for SRDF/S (Synchronous) where presented.


SRDF Overview Mod 2


Closing Slide

This concludes, Module II SRDF/S (Synchronous) for Symmetrix Business Continuity SRDF Solutions.

Symmetrix Business Continuity SRDF SolutionsModule Objectives SRDF/S SynchronousSymmetrix Remote Data Facility (SRDF)SRDF Source and Target VolumesRemote Link Director (RLD)SRDF GroupsSRDF Link ConfigurationFibre Link Point-to-point CampusFibre Link Switched CampusFibre Link Extended DistanceTypical SRDF Extended Distance InfrastructureNative GigE and iSCSI supportSRDF ConnectivitySRDF - Modes of OperationsSRDF Modes of OperationSRDF Modes of OperationSRDF Modes of OperationSRDF Modes of OperationSRDF Modes of OperationSRDF Level of SynchronizationSRDF SerializationAdaptive Copy Disk ModeDynamic SRDFR1/R2 SwapConcurrent SRDFConcurrent SRDFModule SummaryClosing Slide

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