I want to create an Elasticsearch cluster without replica because the cluster is created in a VMinfra and the VMInfra is fully redundant and the Disks are configured in RAID.
Is it fine? also What will be the advantage of creating a cluster without a replica?
Replicas increase availability. So let's say you have a data node that's overloaded or down, if you have another node with a replica of the same shard on it, your data will still be available. I'm not familiar with VMInfra so I'm not sure whether "fully redundant" means you can get the same level of availability in those cases.
For most production uses you'll want to have at least one replica for each shard - meaning, the primary is on one node, and the replica is on another, and therefore at least two separate data nodes. Having more replicas might make sense as load increases. Replicas have costs in memory and disk space - you're essentially storing the data several times.
Having not any replica shards even in optimistic view is bad trade off, Replicas provide redundant copies of your data to protect against hardware failure beside that they are increasing the throughput of your query results because the queries executed on all replicas in parallel with out interrupting each others so they also tune your search performance, On the other hand having too many shards can makes your system to overhead.
If your virtual server environment has good configuration i recommend to always have at least one replica shards on the different hard drivers. You may find out more on pros and cons in Here and an old discussion on how replica shards work on this stackoverflow chat.
