[GitHub] [ozone] elek commented on pull request #2331: HDDS-5247. EC: Create ECReplicationConfig on client side based on input string

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elek commented on pull request #2331:
URL: https://github.com/apache/ozone/pull/2331#issuecomment-862142935


   Thanks for the question/suggestion @arp7 and @umamaheswararao. I also considered throwing an exception instead of printing out a warning, but finally, I decided to put only a warning here. Let me share my view here:
   
    1. First of all it's a client-side change. Any serious validation should be placed on the server/OM side. (from this point of view even warning can be removed)
   
    2. It's hard to predict all the possible use cases. I agree that we should introduce a configuration option to make it possible for vendors to limit the available ReplicationConfig/ECReplicationConfig set. But the Apache Ozone code should be as much flexible as possible (IMHO). Example: earlier we hard-coded support of `ONE`/`THREE` replication scheme for closed containers, but it turned out that there is a demand to use other values (like `TWO`)
   
   3. There or other meaningful combinations: for example if dozens of nodes are available and the key sizes are bigger, it may be reasonable to use `6-4` instead of `3-2`. The write amplification is the same, but `6-4` can have better durability (in exchange for more padding + memory usage).
   
   4. I can imagine even 10-10 as a useful option with very specific/smart placement policies (one may require more parity to place them to other racks). But I admit it would be a very rare case.
    
   My suggestion:
   
   Remove the warning from here and put a server-side validation based on the configuration value. I am fine to restrict it to 3-2,6-3,10-4 by default, but power users can modify the defaults if they require it.
   
   Will create this follow-up jira if no objection.


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