Cost four DR patterns against one pair of objectives

short · 40 min · Objective 3.2

Task

Take one workload, state an RPO and an RTO, and work out which of the four standard patterns is the cheapest that meets them -- then show what the other three would cost. Picking a more expensive pattern than the objectives require is a wrong answer, not a safe one.

Steps

  1. Describe the workload in lab/dr.md: its components, its data volume, its normal running cost, and the business impact per hour of downtime.
  2. State an RPO and an RTO, and say where each came from -- a business impact analysis, a contract, or an assumption you are flagging.
  3. For each of backup-restore, pilot light, warm standby and active-active, estimate the achievable RPO and RTO and the monthly standing cost. Record in lab/dr-patterns.csv.
  4. Identify the cheapest pattern that meets both objectives, and state the margin by which it meets them.
  5. Add a row for the failure the lesson warns about: check whether the DR region's QUOTAS would allow full production scale, and what the lead time is to raise them.

Verify

awk -F, 'NR>1 && NF>=4 {n++} END {print n" pattern(s) costed"}' lab/dr-patterns.csv
grep -Eci 'rpo' lab/dr.md
grep -Eci 'rto' lab/dr.md
grep -Eci 'quota' lab/dr.md lab/dr-patterns.csv

Four patterns costed, both objectives stated with a source, and the quota check present. The quota is the detail that fails real DR tests for a reason nobody anticipated.

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