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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