is there any property for tolerance if one region server goes down and only 2 region server can manage meanwhile the region server gets up..

[#1]

Can you please clarify the scenario that you're concerned about? It's not clear at all to me what you're looking for.

[#2 · Accepted solution]

@shakir mulani HBase does the load balancing for you when a regionserver goes down. When this happens, hbase master will resign all the regions from the failed regionserver to other available region servers.

[#3]

As an end user, you may not even notice that a region server goes down without having monitoring watching for it. HBase is very resilient, I've accidentally killed half of the region servers in a small dev cluster and the only noticeable outcome was that Hbase responded slower.