What is sap system refresh when and why it is done?

System refresh and client copy can be the same thing.  Normally when you want to refresh a system this normally means refreshing the clients using a client copy like SCCL or SCC8.  

A system "copy" is very different as this is far more involved than a simple "client refresh" 
  
Imagine you have a DEV and a PRD system and after 6 months the data in DEV is very old so you would perform a client copy SCC8 from PRD to DEV using a profile that copies the application data from PRD to DEV - it actually deletes the data and replaces it with data from PRD.  If however your DEV system died and needed to be completely rebuilt, you would use "Homogeneous System Copy" - you install the OS, Database and SAP and then process the system copy - which makes a complete copy of PRD (all clients) 
  
Client copy - a single client refresh from PRD to DEV - can be just application data, or user data, or configuration or any combination you choose system copy - all clients 100% copied PRD to DEV

 

The system refersh is nothing but the deletion of the client and replacing the data from other client.   

For example : you have clients 100, 200 and 300.  Suppose when you want to refresh the client 100 you remove the client 100 and replace it with 200 0r 300 as per your requirement. Mostly the refresh of clients will be happen at the time of development stage.

System Refresh is a simplified term to Client Copy. Client Copy means copying the production client on to the quality to test the real data. As recommend by SAP this need to carried out every 3 months.

 

The process to carry out the same is as follows: 
 
 1. Create a client on quality system using txn scc4 
 2. Create a RFC between Production system and Quality System (need to create on quality system) 
 3. Login to the newly created client using sap* and pass as a password 
 4. Txn sccl to start the client copy. You can test the client copy by selecting the test run option. (test run will estimate the time taken for the activity).