maximum number RDF devices per RDF group

Why is there a limit on Dynamic RDF devices at all? And what exactly is an RDF group?

Effectively there is not an RDF device limit. If you look at the overall maximum number of devices for the array it it also 64K.

To learn more about RDF groups, check out the "SRDF Groups" section in the SRDF product guide here

Just to be clear, the limit is in fact on all devices in the storage array and not specifically on RDF devices?

I've read the SRDF product guide in the section you pointed out, thank you very much for that by the way. What I understood is that there are three RDF groups - RDF1, RDF2 and Dynamic RDF groups, and inside them can be several types of devices such as R1, R11, R21, R2, R22 (support for certain devices is dependant on the enginuity version and on the RDF group). Can you confirm my understanding of the subject?

Correct, all host devices can be RDF.

RDF1 and RDF2 groups are more historic these days. All RDF groups in VMAX and above will be Dynamic.

Just a small correction... there are 3 types of RDF groups (not 3 groups) . There can be many DYNAMIC RDF groups defined in an array.

What do you mean by "all host devices can be RDF"?

Why are RDF1 and RDF2 more historic these days?

Could you explain why I would want to create multiple Dynamic RDF groups in an array?

Thankyou so much for the help!

Any symdev than can be presented to a host channel ( FA, iscsi of Ficon port) can be made RDF capable. There are internal only devices in the array so that it what I made the distinction "host devices"

Dynamic RDF groups are user creatable. Prior to Dynamic groups they were considered static and could only be created by EMC.

There are many reasons to have more than one RDF group. SRDF/A and SRDF/S modes cannot both be active on the same RDFG at the same time for example.

I recommend you have a read of the SRDF Product guide and the Solutions Enabler SRDF Family CLI User Guide to understand more about SRDF groups.

Got it. In the previous topic, I asked you the same question, didn't pay attention, sorry.

I see why I would want to use several RDF groups when I'm implementing relatively complication solutions such as SRDF/Star, but I really don't see why, for instance,  I would want to create more than one dynamic RDF group per storage array in a SRDF/S solution.

A unique RDF group if you need to replicate between different target arrays, or if you have multiple RDF adapters and you want to have some devices use one set of RDF adapters and another set of devices use another set of RDF adapters.

So if I have different arrays then I will use different RDF groups for organization. However, what about just 2 machines (storage arrays) with SRDF/S, why would I create more than one group per array?

What do you mean by RDF adapters? Why wouldn't I just share all the adapters among one group?

LearnEverything wrote:

So if I have different arrays then I will use different RDF groups for organization. However, what about just 2 machines (storage arrays) with SRDF/S, why would I create more than one group per array?

you typically wouldn't for SRDF/S where you can manipulate RDF relationships separately (versus SRDF/A). For example look at the below configuration. I am using 4 RF adapters between array 1234 and 9999, same RA rdfg group 9. We started out with 2 adapters but then upgraded to 4 to give us better write response times on SRDF/S devices.

symcfg -sid 1234 list -ra ALL -switched


Symmetrix ID: 000000001234 (Local)


            S Y M M E T R I X    R D F    D I R E C T O R S




         Local            Group      Link              Remote            
--------------------- -------------- ---- -------------------------------
        Po                                                    Po         
         r                      FLGS FLGS                      r         
Ident    t  RA Grp  T Name       SH   SH  SymmID       Ident   t  RA Grp 
------  -- -------- - -------------- ---- ------------ ------ -- --------


RF-1E    4        - -     -      --   --  -            -       -        -
         5        - -     -      --   --  -            -       -        -
         6        - -     -      --   --  -            -       -        -
         7   3 (02) D 1234to5678 ..   X.  000197805678 RF-3E   7   3 (02)
         7  10 (09) D 1234to9999 ..   X.  000196709999 RF-1F   7  10 (09)


RF-2E    4        - -     -      --   --  -            -       -        -
         5        - -     -      --   --  -            -       -        -
         6        - -     -      --   --  -            -       -        -
         7  10 (09) D 1234to9999 ..   X.  000196709999 RF-2F   7  10 (09)


RF-3E    4        - -     -      --   --  -            -       -        -
         5        - -     -      --   --  -            -       -        -
         6        - -     -      --   --  -            -       -        -
         7  10 (09) D 1234to9999 ..   X.  000196709999 RF-3F   7  10 (09)


RF-4E    4        - -     -      --   --  -            -       -        -
         5        - -     -      --   --  -            -       -        -
         6        - -     -      --   --  -            -       -        -
         7   3 (02) D 1234to5678 ..   X.  000197805678 RF-2E   7   3 (02)
         7  10 (09) D 1234to9999 ..   X.  000196709999 RF-4F   7  10 (09)

they are in my case but could be in different groups. For example let's say you want to "pin" some devices to use a particular set of RDF adapters because you want to use it for  your ultra response time sensitive devices (Oracle REDO logs for example).  So for those devices you could specify a different group even though it's connecting to the same array.