Hi,
Name Server:
Up to 3 hosts can be configured as MASTER Name Servers (using a “MASTER 1, MASTER 2, MASTER 3” naming designation), while others have to be configured as “SLAVE”. However, in steady state, only one of the “MASTER n” configured hosts has its actual Name Server role as “MASTER” while all other hosts have their actual Name Server roles as “SLAVE”. The MASTER Name Server is responsible for assigning storage/data volumes to active Index Servers at the time they start up.
If the MASTER Name Server host fails, one of the remaining hosts configured as a “MASTER n” Name Server becomes the active MASTER Name Server.
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Its possible more than three but not good practice