Symmetrix Remote Data Facility (SRDF) family of software is the industry’s most powerful suite of remote storage replication solutions for disaster recovery and business continuity designed by EMC.
SRDF transparently remotely mirrors production or primary (source) site data to a secondary (target) site. The local SRDF device, known as the primary (RDF1) device, is configured in a partner relationship with a remote secondary (RDF2) device to form an SRDF pair. By maintaining copies of data in different physical locations, SRDF enables the following operations with minimal impact on normal business processing:
■ Disaster restart
■ Disaster restart testing
■ Recovery from planned outages
■ Remote backup
■ Data center migration
■ Data replication and mobility
Synchronous mode (SRDF/S): the source array waits until the target array has acknowledged each write before the next write is accepted, ensuring that the replicated copy of the data is always as current as the source. To establish the relation in synchronous mode, the source and target arrays need to be in synchronous distances (less than 200KM). However, the latency due to propagation increases significantly with distance.
Asynchronous SRDF (SRDF/A): transfers changes to the target array in units called delta sets, which are transferred at defined intervals. Although the remote copy of the data will never be as current as the source copy, this method can replicate data over considerable distances and with reduced bandwidth requirements and minimal impact on host performance.
Adaptive Copy Mode: used to do bulk transfer of data on the source array to target array before setting up the SRDF/S or SRDF/A. This ensures both the source and target arrays have the same data.
We will now briefly discuss about Adaptive copy mode, SRDF/S (Synchronous) and SRDF/A (Asynchronous)
Consider a host connected to VMAX array, with 1TB data device allocated to it.
Step: 1 Before you begin, its a best practice to Calculate the peak and average writes that can be expected from that host.
Step: 2 After calculation we have to make sure we have enough network bandwidth to support the peak writes.
Step: 3 Create remote device with same size and configuration(stripped or concatenated) as SRDF is a track level copy.
Step: 4 Enable RDF (dynamic) attribute on both source and target devices.
symconfigure -sid <xxxx> -cmd "set dev <dev-id> attribute=dyn_rdf;" preview -nop
symconfigure -sid <xxxx> -cmd "set dev <dev-id> attribute=dyn_rdf;" commit -nop
Step: 5 Create RDF groups (logical grouping of RDF ports on arrays)
symrdf addgrp –label <Group Name> -rdfg <Group num> -sid <xxx> -dir <7H,8H,9H,10H> -remote_rdfg <Remote Group num> -remote_sid <xxx> -remote_dir <7H,8H,9H,10H>
Step: 6 Now we have to establish RDF link between source and target devices.
(all the data on source site is copied on to remote site using Adaptive copy mode for bulk data transfer initially)
a. Create RDF Pairs
symrdf createpair -sid <xxx> -f <device-file.txt> -rdfg < Group num> -type R1 -invalidate R2 -RDF_mode acp_disk
b. Query the RDF pairs
symrdf -sid <xxx> -f <device-file.txt> -rdfg < Group num> query
Step:7 Now we will establish RDF relation between source and target devices.
symrdf -sid <xxx> -f <device-file.txt> -rdfg < Group num> establish -full
Step: 8 Query to see if there are any invalid tracks (or less invalid tracks) at the remote device)
symrdf -sid <xxx> -f <device-file.txt> -rdfg < Group num> query -i 5 -c 10
Step: 9 Now change the mode to SRDF/S or SRDF/A to establish DR.
symrdf -sid <xxx> -f <device-file.txt> -rdfg < Group num> set mode sync (Synchronous) symrdf -sid <xxx> -f <device-file.txt> -rdfg < Group num> set mode async (Asynchronous)
Step: 10 To make the target array accessible to remote host we have to split the RDF link, after which the target array will be changed from write disabled state to write enable state.
symrdf -sid <xxx> -f <device-file.txt> -rdfg < Group num> split