HPE Storage Users Group

Migrating to Synchronous Long Distance replication
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Author:  KeirL [ Fri Jul 12, 2019 3:23 am ]
Post subject:  Migrating to Synchronous Long Distance replication

We have two sites, each with a 3PAR 8200 running 3.2.2 which are in a remote copy relationship using RCIP Asynch periodic as the link can't sustain anything different. We have about 4 vv's that are replicated from site 1 to site 2 in that direction only - I'd estimate about 50TB of data.
We now have a new site (site 3) also with a 3PAR 8200 (again on 3.2.2) which has links to site 1 that can sustain synchronous replication using RCIP.

I would like to replicate these same 4 vv's to site 3 as well as site 2 and believe I can use SLD for this.
Is it possible to transition from an existing 1:1 RC relationship to an SLD configuration without having to break the existing RCG between site 1 & 2. What I need to avoid is having to resynch the volumes between sites 1 and site 2. I'm know there will be need for site 3 to have a full synch but that's ok.

thanks in advance

Author:  MammaGutt [ Fri Jul 12, 2019 3:51 am ]
Post subject:  Re: Migrating to Synchronous Long Distance replication

I'm guessing you've not read this. https://h20195.www2.hpe.com/V2/GetPDF.a ... 318ENW.pdf

Read the section on Steps for Converting from an existing 1:1 Remote Copy Configuration to an SLD Remote Copy Configuration

The example is going from 1:1 sync to SLD but it also states The following steps show how to add RCIP Remote Copy targets to the existing Remote Copy 1:1 configuration in our example. It doesn’t
matter whether you are converting a Periodic Asynchronous 1:1 to SLD or a synchronous 1:1 to SLD, these steps are the same.

Just ensure that you're not running out of ports on your 8200s. With only 1Gbit RCIP port I would not use anything other than FC ports for sync replication and doing that without an additional HBA would be a bad idea.

Author:  KeirL [ Fri Jul 12, 2019 4:04 am ]
Post subject:  Re: Migrating to Synchronous Long Distance replication

Brilliant - thanks for the fast reply and the doc - I hadn't seen that. I think that will give me everything I need as far as the approach goes.
I'll need to consider the port concerns as well (as you mentioned), but I think I can find my way through that one.

thanks again

Author:  MammaGutt [ Fri Jul 12, 2019 4:14 am ]
Post subject:  Re: Migrating to Synchronous Long Distance replication


If you take into account persistent ports and fabric redundancy, you will use all your 4 FC ports for hosts. If you use 2 of these for RCFC you will lose persistent ports or fabric redundancy.
RCFC requires dedicated ports for each target and does not support persistent ports.
I'm guessing you're already using both onboard RCIP ports for async replication.
You can fan-out the RCIP ports, but doing both async and sync over the same ports will cause sync RC latency when async snapshot is being transferred. Increased RC latency on sync replication will result in increased write latency for everything in sync replication and port speed of RCIP ports may/will be the limiting factor of the overall performance of the arrays.

So you can do it without additional ports, but it will come at a cost.

Author:  KeirL [ Tue Jul 16, 2019 3:49 am ]
Post subject:  Re: Migrating to Synchronous Long Distance replication

yep - thanks

Just following on from this. It has now been decided to retire the 3PAR at site1 in the near future. So (just to recap) with the SLD in place I will have site1 as the primary site replicating about 5 vv's to both site 2 (asynch periodic) and site 3 (synchronous). Once everything is in synch across all sites I then need to decommission site 1 and so need site 2 and site 3 to retain a 1:1 RC relationship with these same 5 virtual volumes. I understand that in an SLD configuration there is a 'link' between sites 2 & 3 to offer additional redundancy - with this allow me to revert from the SLD configuration to a 1:1 configuration BUT to have the primary now at site 3 replicating (asynch periodic) to site 2 only.


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