Business Continuity Metrics — RPO, RTO, MTBF, MTTR + Site Types
The four continuity metrics on CompTIA Network+ (N10-009) — RPO, RTO, MTBF, MTTR — plus cold/warm/hot site types and how a real change/incident/DR runbook uses them.
- **RPO** = how much data you can lose (backup interval). **RTO** = how long you can be down. **MTBF** = how often things fail. **MTTR** = how long a fix takes.
- Site types by cost + speed: **cold** (empty room, days) → **warm** (some gear, hours) → **hot** (live mirror, minutes) → **cloud DR** (variable).
- The exam trap is confusing RPO with RTO. RPO looks *backward* (time before the outage — data loss). RTO looks *forward* (time after the outage — recovery).
Why this is on N10-009
CompTIA moved business-continuity vocabulary heavily into N10-009. Expect scenario questions like “The CFO says the org can lose no more than 15 minutes of transactions. Which metric is she describing?” — the answer is RPO, not RTO. You need to know the difference cold.
The four metrics
RPO — Recovery Point Objective
How much data are you willing to lose?
Measured in time — “15 minutes of transactions” or “24 hours of email”. RPO directly drives your backup frequency. If RPO = 1 hour, you back up (or replicate) at least every hour.
Mental picture: RPO is a line drawn backwards from the outage. Everything between that line and the outage is data lost.
Backup Backup Backup [OUTAGE]
|----1hr---|----1hr---|----1hr---→ RPO = 1 hour
↑
up to 1hr of data lost
RTO — Recovery Time Objective
How long can you be down?
Measured in time — “4 hours to bring the payroll system back up”. RTO drives the DR architecture: cold site (long RTO OK), hot site (minutes RTO required).
Mental picture: RTO is a line drawn forward from the outage. If you’re not back up by then, you missed SLA.
[OUTAGE] ..... service restored
↑ ↑
start RTO = time-to-recover
MTBF — Mean Time Between Failures
How often does this piece of gear fail?
Reliability metric from the manufacturer. Higher = more reliable. A router with MTBF 200,000 hours will, on average, fail every ~23 years. You use MTBF for capacity planning and spare-count decisions.
MTTR — Mean Time To Repair (or Restore)
When it fails, how long to fix?
MTTR includes detection + travel + repair + verification. If MTTR is 4 hours and MTBF is 200,000 hours, availability ≈ MTBF / (MTBF + MTTR) → very close to 100%.
Site types (DR)
| Site type | What’s there | Bring-up time | Cost |
|---|---|---|---|
| Cold | Space + power + cooling. No gear installed. | Days to weeks. | Cheapest. |
| Warm | Some hardware, partial config, stale data. | Hours. | Middle. |
| Hot | Fully live mirror, real-time replication. | Minutes. | Expensive. |
| Cloud DR | Compute + storage in AWS/Azure/GCP, ready to spin up. | Minutes to hours depending on tier. | Variable — pay for compute only when failover happens. |
If the exam scenario says “tight RTO, budget-constrained, mostly-idle DR” → cloud DR. If it says “regulatory requirement for near-zero downtime” → hot site. If it says “large industrial with days-long tolerance” → cold site.
Related terms you’ll see
- MTBSI — Mean Time Between System Incidents. Similar to MTBF but for the system, not the component.
- SLA (Service Level Agreement) — the contractual availability target. “Four nines” = 99.99% = 52 minutes downtime/year.
- BCP (Business Continuity Plan) — the whole document that says what stays running during a disaster.
- DRP (Disaster Recovery Plan) — the technical playbook to restore IT after a disaster. Subset of the BCP.
Common exam traps
- Confusing RPO with RTO. RPO = data loss tolerance (looks backward). RTO = downtime tolerance (looks forward). This is the #1 tested distinction.
- Assuming a hot site means zero data loss. A hot site with async replication still has an RPO > 0. Only synchronous replication gets you RPO = 0 (and it’s expensive at latency-sensitive distance).
- Mixing up MTBF and MTTR. MTBF is between failures (reliability). MTTR is during a failure (recovery). Both are means / averages.
- Ignoring people/process cost. DR isn’t just gear. The exam expects you to know that runbooks, training, and failover drills are part of BCP.
Real runbook shape
A production DR runbook typically has:
- Trigger criteria (what counts as a disaster?)
- RPO / RTO targets per system
- Roles + call tree
- Failover steps (per system, in dependency order)
- Failback steps (once primary is restored)
- Post-incident: RCA + runbook update
Cheat strip
RPO backward data loss tolerance drives backup freq
RTO forward downtime tolerance drives DR site type
MTBF between failures reliability (high=good)
MTTR during a failure recovery speed (low=good)
Cold space only days cheap
Warm partial gear hours middle
Hot live mirror minutes expensive
Cloud DR pay-per-use variable flexible
BCP = the whole plan | DRP = the technical subset
SLA "four nines" = 99.99% = 52 min downtime/year
Cable Connector Types — Copper, Fiber, Coax
Every connector CompTIA Network+ (N10-009) shows in exam images: RJ45, RJ11, F-type, BNC, SC, LC, ST, MTRJ, MPO, LC-APC vs LC-UPC. What each pairs with and the one-line 'how to tell them apart' rule.
Twisted-Pair Cable Categories — Cat 5, 5e, 6, 6a, 7, 8
Every twisted-pair category CompTIA Network+ (N10-009) tests: max speed, max distance, PoE class, when to pick each. Plus the shielding letters (U/UTP, F/UTP, S/FTP) that trip up half the room.
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