Elastic stack hardware requirements, (look for recommendation)

Hi,

I want setting up a cluster and I have these scenarios:

  • 28 servers generate log per daily;
  • EPS logs are 300 /s per server;
  • EPD logs are ~5MM/day;
  • RAW DATA BYTES is ~ 460BYTES;
  • Size GB Day ~ 1.2TB;

My required retention period is about 30 days.

EPS is 300 per host means global EPS is 8400 (300 * 28)
Means also an EPD of 725M and a total daily raw data of 310 GB, why 1.2 TB ?
Is my understanding correct ?
What's the required retention period ? 30 days , 90 days ...