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Interview Questions and Answers
SRDF - Possible Questions for Interview

What is Business Continuity?

Business Continuity is the preparation for, response to, and recovery from an application outage that adversely affects business operations.

What are the Business Continuity tools available for symmetrix?

Power path at host end TimeFinder/Mirror, Clone and Snapshot for local replication SRDF for remote replication.

Business Continuity addresses what?

Business Continuity Solutions addresses systems unavailability, degraded application performance, or unacceptable recovery strategies.

What is RPO and RTO?

RPO refers to the maximum amount of data loss an application can tolerate as measured in time. In other words, the amount of data loss that can be tolerated (cost of transaction versus risk).

RTO refers to the maximum time a company budgets to bring an application back online in the event of a disaster. In other words, the time it takes to recover the data once a disaster or other recovery event is declared (risk versus cost)

What are the different types of Device Groups?

Regular, RDF1, RDF2 and Composite group

Briefly explain baout Regular, RDF1 and RDF2 device groups?

Regular device groups are normally used for TimeFinder operations
RDF1 and RDF2 device groups are normally used for SRDF operatins

What is composit group?

A composite group is a user-defined group of device members that can span multiple Symmetrix arrays and SRDF groups. The CG type may be defined as REGULAR,RDF1, RDF2, or RDF21, and may contain various device lists for standard, BCV, virtual (VDEV), RBCV, BRBCV, second hop standard, and second hop BCV.

What is the difference between TimeFinder and SRDF?

Time Finder is for local replication operations
SRDF is for remote replication operations

What are the different types of Remote Link directors used for SRDF?

RF (Fibre Channel directors)
RA (ESCON directors)
MPCD (Multiprotocol Channel Directors) available with these channel connections
FICON
iSCSI for host
GigE (RE) for SRDF

How many dynamic RDF groups can be created in an array?

Symmetrix DMX supports up to 64 total RDF groups.

What are the different types of Link configurations for SRDF?

Unidirectional: If all primary (source or R1) volumes reside in one Array and all secondary (target or R2) volumes reside in another Array, write operations move in one direction, from primary to secondary. Data moves in the same direction over every link in the SRDF group.
Bidirectional: If an SRDF group contains both primary and secondary volumes, write operations move data in both directions over the SRDF links for that group.
Dual-Directional: 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

How the SRDF synchronous mode of operation works?

Write I/O received from host/server at the source
The I/O is transmitted to the target
An acknowledgment is provided by target back to the source
The I/O is serviced to the host

How the SRDF semi synchronous mode of operation works?

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

How the SRDF Adaptive copy mode of operations works?

Write I/O received from host/server at the source
The I/O is serviced to the host I/O accumulates in/onSymmetrix cache in Write Pending Mode R1 volumes in Disk Mode.
I/O is transmitted to the target.
An acknowledgment is provided by target back to the source.

What is Writing Pending and Disk Mode of Adaptive Copy?

I/O is accumulates in Symmetrix cache in Write Pending Mode
I/O is accumulates in R1 volume in Disk Mode

What is the purpose of Adaptive copy mode?

Adaptive Copy Mode is used primarily for data migrations and data center moves.

How the SRDF Asynchronous mode of operation works?

Write I/O received from host/server at the source
The I/O accumulates in Source Symmetrix cache
The I/O is serviced to the host
The I/O is continually transmitted to the target
The I/O accumulates in Target Symmetrix cache

What is SRDF Domino mode?

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.

How the SRDF domino mode works?

Write I/O received from host/server at the source
The I/O fails to transmit to the target
Both Source and Target become unavailable

How many R2 devices can be paired with one R1 device concurrently?

Two

What are the restrictions of SRDF device group?

All devices in a disk group must be in the same Symmetrix ICDA
All devices must be of the same type (RDF1, RDF2, Regular)
A device can only belong to a single Device Group per SYMAPI database

How do you check the connectivity status of SRDF link?

Symrdf –sid "SymID" ping
Symrdf –sid "SymID" -RA list all

What are the disaster recovery operations?

Failover: from the source side to the target side, switching data processing to the target side.
Failback: from the target side to the source side by switching data processing to the source side.
Update: the source side after a failover while the target side may still be operational to its local host.

How will failover operation works?

Write Disable device(s) on SA at source (R1)
Suspend RDF link(s)
Read/Write Enable device(s) on RA at target (R2)

How will update operation works?

Suspend RDF link(s)
Merge device track tables between source and target
Resume RDF link(s)

How will failback operation works?

Write Disable device(s) on RA at target (R2)
Suspend RDF link(s)
Merge device track tables between source and target
Resume RDF link(s)
Read/Write Enable device(s) on SA at source (R1)

What are the decision support SRDF operations?

Establish:
Resume Normal SRDF operations
Preserves data on the source (R1) volumes, discarding changes to the target (R2) volumes

Split:
Suspends link between source (R1) and target (R2) volumes
Enables read and write operations on both source and target volumes

Restore
Resume SRDF operations
Preserves data on the target (R2) volumes, discarding changes to the source (R1) volumes

How the split operation will works?

Suspend RDF link(s)
Read/Write Enable device(s) on RA at target (R2) also.

How will establish operation works?

Write Disable device(s) on RA at target (R2)
Suspend RDF link(s)
Resume RDF link(s)
Merge device track tables between source and target
Resume RDF link(s)

How will restore operation works?

Write Disable device(s) on SA at source (R1)
Write Disable device(s) on RA at target (R2)
Suspend RDF link(s)
Merge device track tables between source and target
Resume RDF link(s)
Read/Write Enable device(s) on SA at source (R1)

Can you briefly explain about SRDF/S?

SRDF/S is a configuration of multiple Symmetrix units that maintains real time copies of logical volume data in more than one location.
Facility for maintaining real-time or near-real-time physically separate mirrors of selected volumes.
Uses no host CPU resources – Mirroring done at the storage level
Operating system independent
There is a performance impact on arrays
Limited distance

Can you briefly explain about SRDF/Asynchronous?

The Symmetrix array provides a consistent point-in-time image on the target (R2) device, which is a short period of time behind the source (R1) device. Managed in sessions, SRDF/A transfers data in predefined timed cycles or delta sets to ensure that data at the remote (R2) site is dependent write consistent.
SRDF/A provides a long-distance replication solution with minimal impact onperformance that particularly preserves data consistency with the database.
Promotes efficient link utilization resulting in lower link bandwidth.
Maintains a dependent write consistent copy on the R2 devices at all times.
Supports all current SRDF topologies, including point-to-point and switched fabric.
Requires no additional hardware, such as switches or routers.
Supports all hosts and data emulation types supported by the Symmetrix array
Minimizes the impact imposed on the back-end DA directors.
Provides a performance response time equivalent to writing to local non-SRDF devices.
Allows restore, failover, and failback capability between the R1 and the R2 sites.

What are the factors that effects the SRDF/A implementation?

SRDF link Bandwidth, Symmetrix Cache and Workload.

What is SRDF Automated Replication?

SRDF/AR allows users to automate the sequence of SRDF and TimeFinder mirror operations. The automated sequence, cycle, is performed on a user-defined interval called cycle time. it is usually set to operate in Adaptive Copy mode due to the long distance between local and remote sites. This allows the users to save on network bandwidth thus minimizing the network costs without compromising the integrity of the data.
Allows business restart site to be at any distance away from source
Collaboration of SRDF and TimeFinder commands
Minimizes network costs

How do you change or set the SRDF mode of operations?

Examples:
symrdf -g "DgName" set mode sync
symrdf -cg set mode semi
symrdf -f FileName set mode async
symrdf -g "DgName" set domino on
symrdf -g "DgName" set domino off
symrdf -g "DgName" set mode acp_wp
symrdf -g "DgName" set mode acp_off
symrdf -g prod set mode acp_disk
symrdf -g prod set mode acp_off

What is the background process during the SRDF pairs full establish?

The target (R2) device is Write Disabled to its local host I/O.
Traffic is suspend on the SRDF links.
All the tracks on the target (R2) device are marked invalid.
All tracks on the R2 side are refreshed by the R1 source side. The track tables are merged between the R1 and R2 side.
Traffic is resumed on the SRDF links.

What is the background process during the failback?

The target (R2) device is Write Disabled to its local hosts.
Traffic is suspended on the SRDF links.
If the target side is operational, and there are invalid remote (R2) tracks on the source side (and the force option is specified), the invalid R1 source tracks are marked to refresh from the target side.
The invalid tracks on the source (R1) side are refreshed from the target R2 side. The track tables are merged between the R1 and R2 sides.
Traffic is resumed on the SRDF links.
The source (R1) device is Read/Write Enabled to its local hosts

How will the SRDF restore operation works?

The source (R1) device is Write Disabled to its local hosts.
The target (R2) device is Write Disabled to its local hosts.
Traffic is suspended on the SRDF links.
All tracks on the source (R1) device are marked as invalid.
All R1 tracks are refreshed from the R2 side. The track tables are merged between the R1 and R2 side.
Traffic is resumed on the SRDF links.
The source (R1) device is read/write enabled to its local hosts.

Explain step by step procedure to perform SRDF/S?

SRDF/S normal operations
Creating device groups in source and target Arrays:
symdg -type RDF1 create "SourceDgName"
symdg -type RDF2 create "TargetDgName"

Adding devices R1 and R2 devices to source and target device groups
symld -g "SourceDgName" add dev "SymDevName"
symld -g "TargetDgName" add dev "SymDevName"

Setting SRDF mode of operation:
symrdf -g "DgName" set mode sync

SRDF normal operations:
symrdf -g "DgName" suspend
symrdf -g "DgName" resume

SRDF/S disaster recover operations
symrdf -g "DgName" failover
symrdf -g "DgName" update -remote
symrdf -g "DgName" failback

SRDF/S decission support operations:
symrdf -g "DgName" split
symrdf -g "DgName" restore
symrdf -g "DgName" establish

Explain step by step procedure to perform SRDF/Asynchronous?

Creating RDF group:
symrdf addgrp -label -rdfg "GrpNum" -sid "SymID" -dir "DirNum" -remote_sid –remote_dir -remote_rdfg "RemoteRdfgNum"

Create device pair:
symrdf -file "DevFileName" -sid "SymID" -rdfg "GrpNum" -type r1 -establish -g "DgName" createpair –noprompt

Changing SRDF mode :
symrdf -g "DgName" set mode async -noprompt

Explain step by step procedure to perform SRDF/AR for single hop?

Create a device group:
symdg create "DgName" -type regular

Add the standard device to the device group:
symld -g "DgName" add dev "SymDev"

Associate the R1/BCV device:
symbcv -g "DgName" associate dev "SymBcvDev"

Associate the remote BCV device:
symbcv -g "DgName" associate dev -rdf -bcv

Prepare the mirror states and start the session:
symreplicate -g "DgName" start -option "Path" -setup -consistent

Stop the session:
symreplicate -g "DgName" stop -nop

Restart the session:
symreplicate -g "DgName" restart -nop

OR

Create a device group:
symdg create "DgName" -type regular

Add the standard device to the device group:
symld -g "DgName" add dev "SymDev"

Associate the R1/BCV device:
symbcv -g "DgName" associate dev "SymBcvDev"

Associate the remote BCV device:
symbcv -g "DgName" associate dev "SymBcvDev" -rdf -bcv

Establish the STD and R1/BCV:
symmir -g "DgName" establish -full

Split the STD and R1/BCV:
symmir -g "DgName" split -consistent

Resume SRDF link:
symrdf -g "DgName" resume -bc

Establish the R2 and remote BCV:
symmir -g "DgName" est -full -rdf -bcv

Split the R2 and remote BCV:
symmir -g "DgName" split -full -rdf -bcv

Establish the STD and R1/ BCV:
symmir -g "DgName" establish

How the symstar will be configured?

Uses concurrent and cascaded SRDF/Synchronous and SRDF/Asynchronous links to replicate source data synchronously to a nearby regional site and asynchronously to a distant remote site.

How do you recover suspended or partitioned state session?

Using symrecover command.

What are the access rights required if ACLs enabled?

BASE and CFGSYM access rights required.

Can we migrate the R1 data to larger R2 device?

Yes, we can migrate the R1 data to larger R2 but we can not perform device swap, SRDF/Star operations, we can not restore back to the R1 device and Concatenated meta devices are not supported.

How do you create groups for dynamic RDF pairs in a device file?

Creating dynamic pairs in a device file:
symrdf createpair -file "DevFileName" -sid 55 -rdfg 2 -type rdf1 -invalidate r2 -g "DgName"

What is dynamic R1/R2 swap?

The dynamic R1/R2 swap feature swaps the SRDF personality of the SRDF device designations of a specified device or composite group

What is link limbo and how do you specify?

feature allows you to set a specific length of time for Enginuity to wait when a down link is detected before updating the link status. If the link status is still Not Ready after the link limbo time expires, devices are marked Not Ready to the link.
symrdf -sid 80 -rdfg 4 set link_limbo 60

How do you create/add the dynamic SRDF group?

symrdf addgrp -label "RdfGrpName" -rdfg "RdfGrpNum" -sid "SymID" -dir "DirNum" -remote_rdfg 4 -remote_sid "SymID" -remote_dir "RemDirNum"

How do you add dynamic SRDF pairs to dynamic SRDF group?

symrdf createpair -file "DevFileName" -sid "SymID" -rdfg "RdfGrpNum" -type rdf1 -invalidate r2

What are the Symmetrix Array-wide parameter in SRDF/A?

Maximum SRDF/A Cache Usage and Maximum Host Throttle Time

How do you set the metrics on symmetrix for SRDF/A?

set symmetrix rdfa_cache_percent = 94;
set symmetrix rdfa_host_throttle_time = 0;

What is RDF group session priority parameter?

When SRDF/A needs ts drop sessions when the cache WP limit is reached, the sessions will be dropped starting with priority values of 64 with a setting of 1 being the last to be dropped.

What is the SRDF mode of operation for SRDF/AR?

Adaptive copy mode.

What are the required options for symreplicate options file?

SYMCLI_REPLICATE_HOP_TYPE and one of SYMCLI_REPLICATE_CYCLE or SYMCLI_REPLICATE_CYCLE_DELAY

What is consitency and how to enable?

Consistent split allows us to avoid inconsistencies and restart problems that can occur if you split a database-related BCV without first quiescing the database.
symrdf -g enable

What is automatic tripping and manually tripping of composite group?

Automatic Tripping - Occurs when one or more R1 source devices in an consistency enabled Composite Group cannot propagate data to their corresponding target devices.
Manual Tripping - Occurs when you invoke the symrdf –cg suspend or split command.

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