- IBM Metro Mirror
- PPRC Commands
- EMC SRDF mirroring
- SRDF Commands
- HDS Universal Replicator
- Global Mirror
- z/OS Global Mirror
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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.
symcfg list -ra all
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.
symrdf addgrp -label rdfg02 -rdfg r1_devg_001 -sid 1234 -dir 1A -remote_rdf r2_devg_001 -remote_sid 5678 -remote_dir 2A
symrdf -file rdf_list.txt -sid 1234 -rdfg r1_devg_001 createpair -type RDF1 -invalidate r2 -rdf_mode acp_disk -nop
symrdf list -rdfg r1_devg_001
symrdf -file rdf_list.txt establish -full -rdfg r1_devg_001 -sid 1234
symrdf -file rdf_list.txt -rdfg r1_devg_001 set mode sync
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.