Can shadow replica improve indexing performance of ES cluster?

If we use a NAS/SAN storage in ES cluster with shadown replica feature, how about the indexing performance?

I thought that es nodes only need to cosume resources for the primary shards, then the indexing performance can imporve to 2x? (Assuming that NAS/SAN can provide a much better IOPS than common NFS or HDFS).

Not sure if you will see a x2 improvement but yes it should be better.