SRDF Commands

The following commands will give you a flavour of how to use CLI commands to set up and manage SRDF. You should consult EMC manuals and your Dell-EMC rep for up to date information. To make the examples easier, I'm assuming you have a local symm with sid 1234 and dir 1A, and a remote Symm with sid 5678 and dir 2A. You will need to use your own values.

Configuring RDF

  1. Planning! Get the current size of the data you intend to replicate and calculate how much growth you expect over the next year or so. The find out how much data is changing each day on average, and see if that will increase with time too. Use these numbers to work out how much network bandwidth you need to transfer that data, ensuring you can cope with peak workloads. Now make sure your cross site network capacity can handle that capacity. The network can be GigE, FC or SAN connectivity.
  2. Configure a remote Symm with devices of the same size and configuration as the primary. The primary disk and target mirror should have identical device characteristics. For example, if 123 is a striped meta device with 4 hypers of 60 GB, then 123 must be a striped meta of the same size.
  3. Check to see if there are any existing RDF Groups with the command below. You may be able to use an existing group.

    symcfg list -ra all

  4. Enable dynamic RDF on both source and target devices.

    symconfigure -sid 1234 -cmd "set dev 123 attribute=dyn_rdf;" commit -nop

    The -nop parameter means no prompt, or don't ask me if I really want to do this.

  5. Create a new pair of RDF groups between two sites, which we will call r1_devg_001 and r2_devg_001.

    symrdf addgrp -label rdfg02 -rdfg r1_devg_001 -sid 1234 -dir 1A -remote_rdf r2_devg_001 -remote_sid 5678 -remote_dir 2A

  6. Create a text file on the management server which lists of source devices and destination devices in pairs. In the example, we will be creating an RDF pair from source devices 121-3 on symmetrix id 1234 to destination devices 221-3 on symmetrix id 5678. So the text file will look like this. We will call the source file rdf_list.txt

      121  221
      122  222
      123  223

  7. Create the pairing between the source and target devices using the above text file. The command below will create pair between the devices mentioned in the text file from source array 1234 using rdf group r1_devg_001. rdf group r1_devg_001 is already configured between Symms ID 1234 and 5678. So the command will pick the destination device 221 from Sym ID 1234 based on the relationship defined in rdfg r1_devg_001. The commad will create the pairs in Adaptive copy mode.

    symrdf -file rdf_list.txt -sid 1234 -rdfg r1_devg_001 createpair -type RDF1 -invalidate r2 -rdf_mode acp_disk -nop

  8. Check the pairing has worked, you will see the pairs in suspended status.

    symrdf list -rdfg r1_devg_001

  9. Start the synchronization of the pairs. Once the below command is completed, execute command in step 5 to verify the status.

    symrdf -file rdf_list.txt establish -full -rdfg r1_devg_001 -sid 1234

  10. Once all the pair are in sync status in Adaptive copy mode you can switch the SRDF mode of operation to the one you require, either aysnc or sync. The command below will switch to sync mode.

    symrdf -file rdf_list.txt -rdfg r1_devg_001 set mode sync

Managing RDF

You could create a disk group and add all source devices into it, then manage the pairs using the disk group name. For example, the below commands create 'dg_001' and add device 123 into it. symdg create dg_001 -sid 1234 -type RDF1 symld -g dg_001 add dev 121 -sid 1234

Once you create an disk group, you can use composite SRDF commands to control all the disks in that group. For example

symrdf -g dg_001 failover

You can use this command to fail the entire disk group over to the DR site. It will Write Disable the source volumes, set the link to Not Ready and Write Enable the target volumes

To Failback, that is restore service to your primary site, use the command

symrdf -g dg_001 failback

This will write disable the target (remote) disks, suspend the RDF link, merge changed disk tracks, resume the link then write enable the source disks.

While failback is in progress, you do not have a remote DR position. You can speed the failback operation up by copying invalid tracks before write disabling any disks with the command

symrdf -g dg_001 update

If you want to split the SRDF managed disks, that is stop mirroring and allow the disks at both sites to be updated independently, then you need the split command. This suspends the RDF link and write-enables the target disks.

symrdf -g dg_001 split

And once you do this, you will probably want to go back to an SRDF mirrored state again, so you need the establish command

symrdf -g dg_001 -full establish

This will write-disables the target disks, suspend the rdf link, Copy data from source to target then resume the rdf link.

The restore command does this the other way around. It will copy the data from the target disk back to the source. The command is

symrdf -g dg_001 -full restore

This write disables both source and target disks, suspends the rdf link, merges the track tables, resumes the rdf link then write enables R1

Other useful commands, which should be self explanatory are;

symrdf -g group-name suspend
symrdf -g dg_001 resume
symrdf -g dg_001 set mode sync
symrdf -g dg_001 set domino on
symrdf -g dg_001 set acp-disk skew 1000

A Consistency Group is a collection of volumes in one or more symmetrix devices that need to be kept in a consistent state. If a write to a Symmetrix cannot be propagated to the Remote Site, the Symmetrix will hold the I/O for a fixed period of time. At the same time it presents a SIMM back to the host. The Congroup STC will detect the SIMM and issue the equivalent of PPRC FREEZE to all the other Symmetrix online to that Host. All Volumes in that consistency Group will then be suspended. Once they are all suspended the equivalent of PPRC RUN is issued and I/O can complete, including the first I/O that triggered the SIMM.
Consistency Group processing with SRDF does not lose data because it employs a FREEZE/RUN approach similar to PPRC FREEZE/RUN.

To create a consistency group, add devices to it and enable it, you use commands

symcg create r1_cg001 -type rdf1
symcg -cg r1_cg001 -sid 1234 add dev 0220
symcg -cg r1_cg001 -sid 0011 add dev 001C
symcg -cg r1_cg001 enable

SRDF data replication software from EMC arguably has better functionality than PPRC, but it used to have one major failing when used on an IBM mainframe, its command set was totally different. What? Well, SRDF commands only work on EMC disks. Other vendors such as HDS took the IBM PPRC command set, and interpreted it to run their own replication software, so the underlying code is different, but the command set is the same. This meant that you could run a disk farm of IBM and HDS disks, and control all the mirroring using one set of commands. EMC did have a half-way solution; you could run a mainframe started task that intercepted the PPRC commands and converted them to SRDF commands before passing them down the channel. This was far from ideal, and prone to error. However, EMC have now joined the fold; they will now accept native PPRC commands at the Symmetrix, and convert them into SRDF commands in the microcode.

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