topic 3par 7200c RCIP : Additional space need for async replication in HPE 3PAR StoreServ Storage

3par 7200c RCIP : Additional space need for async replication

aungshu — Wed, 15 Apr 2015 04:53:46 GMT

Hi,

Can anyone provide me reference doc/information regarding what percentage of additional disk space need for RCIP asyncronous replication.

Let me expalin the scenario. One of our customer production VV is arounf 7 TB ( RAID 1 ) which need to be replicated to the DR site. I came to know that for that storage need additional 7 TB ( it can be RAID 5). But I did not validated this information, I need reference doc/information for the exact requirement.

Can anyone help me ?

BR \\ Aungshu

Re: 3par 7200c RCIP : Additional space need for async replication

Sheldon Smith — Wed, 15 Apr 2015 13:05:31 GMT

Worst case, 7TB. Which means the production volume is full (all 7 TB in use), and all of it has changed since the last "syncrcopy".

Let me explain the scenario. A production VV exists (size doesn't matter). When replication is first started, a virtual copy is created. That virtual copy is transferred over to the destination array where it is written to the DR VV.
In the mean time, the virtual copy grows like any other virtual copy. How much depends on base volume activity. How localized are the changes? If all the activity is taking place in 10% of the base, then the virtual copy will only need 10%. Are other virtual copies being made of the base volume for local use? If so, they will all share the common snapshot data. If something needs to be written to the base volume's copy space, it's only written once. All snapshots simply point to the regions they need.

When the next syncrcopy occurs, a new virtual copy is taken of the base volume. The new and previous virtual copies are compared and only the differences are transferred across. Once the transfer is complete, the previous virtual copy is removed and the space used in the copy CPG is available for reuse. An occasional "compactcpg" can accellerate the process of trimming used space out of the copy CPG back to the system's free pool.

Regards,

Re: 3par 7200c RCIP : Additional space need for async replication

aungshu — Wed, 15 Apr 2015 13:24:27 GMT

Hi Smith,

Thanks for your response with detailed explanation. In this case all the production VV will be full provisioned and RAID 1. Give me a standard idea what will be the percentage need to be free in the storage base for intial replication started as after 1st sync only changed data will be replicated.

Do let me know if you need any other detail information for comments on this.

BR \\ Aungshu

Re: 3par 7200c RCIP : Additional space need for async replication

aungshu — Wed, 15 Apr 2015 13:44:35 GMT

Forget to mention 7 TB will not be the size of 1 vv, under RAID 1 there will multiple vv and total size of all the VV under RAID 1 will be 7 TB.

Please suggest me which will be the standard space that need to be consider in the storage for sucessful replication.

BR \\ Aungshu

Re: 3par 7200c RCIP : Additional space need for async replication

aungshu — Fri, 17 Apr 2015 07:04:53 GMT

Waiting for expert feedback , what will be the consideration of free space for achiveing 7 TB replication ( maximum one LUN or vv size will be 1 TB). And vv will be full provisioned.

BR \\ Aungshu

Re: 3par 7200c RCIP : Additional space need for async replication

Sheldon Smith — Fri, 17 Apr 2015 12:45:36 GMT

There is no magic percentage.

You are talking about a snapshot. How big is any snapshot?

How much space will be used will vary from nothing to the same size as the base volumes.
When a syncrcopy starts, the new snapshot will be empty! Over time the snapshot will grow as needed. The snapshot will continue to grow as needed until the next syncrcopy, at which time a newer empty snapshot will be created and the now old one will be deleted once the syncrcopy finishes.

Beyond that, you are asking someone to guess about the change rate of your data.

How much is changing?
How localized are the changes?
How often do you snaprcopy?

All those are factors in how big the snapshot grows between snaprcopy runs.

So, either 100%, which would allow every byte of the base volume to be filled and/or changed, or some percentage less.

If "some percentage less", if the system runs out of free space, the snapshot will become "stale" and a full copy will need to be redone from source to destination. Then you need to decide how "painful" it is to perform a full copy. So you might want to figure having 70% to 80% of the volumes' size available, at which point you are copying most of the new data anyway.

Note: While I work for HP, all of my comments (whether noted or not), are my own and are not any official representation of the company.
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