Mainframe SRDF

Question

I am a UNIX/Windows guy that will be implementing SRDF/A for the first time. Unfortunately, I have to start off with our z/OS mainframe before I work on the platforms that I am so comfortable with.

I have asked our z systems programmer to provide me with some info regarding which volumes will be replicated and how they will be grouped. I was hoping he would come back with something like this -

volumes bb0-bdf - OS volumes to be replicated every 8 hours

volumes bc0-bff - Application volumes (DB2, VSAM, flat files to be replicated every 30 seconds).

This would allow me to have a minimum of device groups, RA groups and consistency groups. I feel like the fewer of these things to manage the better. Instead, he is coming back with many (8-12) different smaller groups - some with only a few volumes. There are two different applications on the host so I could easily tolerate 1 OS group and 2 application groups. If I have as many as 12 groups each with a device groups, RA group, and consistency group; will this be difficult to manage? Isn't it better to have fewer of these groups?

Once I'm done with the IBM mainframe I will have to tackle our Unisys, Windows and UNIX environments. I feel like I need to keep the complexity to a minimum. What do you think? Any insight to current z/OS SRDF implementations would be great.

Allen Ward · Accepted Answer

We run on a 30 second minimum cycle time, but that occasionally elongates (naturally) when things get really busy. We don't use special consistency groups... we just have the consistency flag turned on for the one RDF group we use.

Allen Ward · Answer

Brad, I have a mixed environment and we have been using SRDF/A for several years now to mirror both z/OS and various Open Systems hosts.

Up until very recently we have had all of our mainframe devices mirrored in a single group. We are currently working to split that into two groups, but only because some of the devices only require acp_disk mirroring and the main group is kept in async mode. We actually have 5 z/OS LPARs (for 5 separate companies) mirroring together in that one group. With the exception of recent issues that prompted moving out the acp_disk devices to a separate group, this has worked well for us. On the Open Systems side we define a group for each major application environment (e.g. SAP, Oracle, etc.) but we only mirror the most critical data over SRDF/A for Open Systems.

brad12341 · Answer

Allen,

Great info. I love the idea that you've been able to live with only one group even for multiple LPARs. We have 1 production LPAR in California and 1 Disaster Recovery LPAR in Texas.

What is you cycle time for sending the changes? It seems like the data would need to go frequently (30 seconds) but any OS changes could be in a different group and go a few times each day.

Do you have any need for Consistiency Groups or can you handle everything with the device groups and RA groups.

Thanks - Brad

SKT2 · Answer

also be sure about what option you need for 'Prevent RAs Online Upon (P)ower On' for the rdfg group.

brad12341 · Answer

Allen, I'm trying to find out about our consistientcy flag.  Is there an smc screen or symcli command that show whether or not it is turned on?

RobertDudley · Answer

if you run a query against the device group you should see under RDF Pair state the word Consistent if you have enabled consistency and the device are cycling properly. Last column on the right side of the window.

symrdf -g devicegroupname query

Allen Ward · Answer

Actually you can have all the devices in a group show Consistent regardless of the status of the Consistency flag. Only the one mainframe group we run (plus one new one with special requirements for VMware SRM) has the Consistency flag set. To see the status of the flag for all groups, use the following command:

symcfg -sid XXXX list -rdfg all

Obviously replace the XXXXwith your SymmID and if you just want to look at one group you can specify it instead of "all". This listing will show some very interesting info on all your groups. Under the FLAGS column near the right side you will see the first column labeled "C". This is the Consistency flag. If there is an "X" in that column then that group has Consistency enabled. The next column over is one I find most useful. If we have had any kind of network connectivity issue affecting our mirroring link this is the first command I run to see if all my groups are still active "A" in asyc mode. It's a quick way to find which ones (if any) I have to focus on.

Symmetrix

Mainframe SRDF

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