Number of machines required in Disaster recovery site in HA arcgis enterprise

[shafitrumboo1]

We have 

1 - Enterprise ArcGIS 10.5 with ArcGIS server federated with ArcGIS Portal

2 - We have two ArcGIS server and two portal machines available trough two Web adapter machines. and these two web adaptors are also HA using hardware load balancer. On every webadpater machine we have two instances one for portal and another for arcgis server.

We want to have DR site do we need have same number of machines at DR site. Here I mean is it mandatory for DR site to HA.?  If not then what can be disadvantage

I went through Disaster recovery and replication—Portal for ArcGIS (10.5.x) | ArcGIS Enterprise  it says the primary and standby environments must be duplicated. Each data center must have the same number of machines

Derek Law‌

[JonathanQuinn]

Your DR site doesn't need the same number of machines, but our recommendation is that it does to avoid any drops in redundancy or performance.

A lot of organizations devote more resources to their primary deployment, though, so I think it'd be common for a standby deployment to have less resources, (as long as the plan is to switch back to the primary once it's brought back online).