Backup, RAID and Recovery
RAID levels and backup types both come down to a trade between speed, capacity and how much you can lose. The tables state each one so a scenario can be matched to it.
Backup, RAID and Recovery · firsttry.app/cheatsheets/backup-and-raid · original reference written from published exam objectives. Not affiliated with any certification body.
RAID levels
| Level | Minimum disks | Fault tolerance | Usable capacity |
|---|---|---|---|
| 0 | 2 | None. One failure loses everything | 100% |
| 1 | 2 | One disk per mirror | 50% |
| 5 | 3 | One disk | Total minus one disk |
| 6 | 4 | Two disks | Total minus two disks |
| 10 (1+0) | 4 | One per mirrored pair | 50% |
Backup types
| Type | Copies | Restore needs | Archive bit |
|---|---|---|---|
| Full | Everything | The full backup only | Cleared |
| Incremental | Changes since the last backup of any kind | Full plus every incremental since | Cleared |
| Differential | Changes since the last full | Full plus the latest differential | Not cleared |
| Snapshot | Point-in-time state | The snapshot. Not a backup on its own | Not applicable |
| Synthetic full | Assembled from a full plus increments | Behaves like a full | Not applicable |
Backup strategy
| Rule | Meaning |
|---|---|
| 3-2-1 | Three copies, two media types, one off site |
| 3-2-1-1-0 | Adds one immutable or offline copy, and zero errors on test restore |
| Grandfather-father-son | Daily, weekly and monthly rotation |
| Immutable backup | Cannot be altered or deleted for a set period. Ransomware defense |
| Air gap | Physically or logically disconnected copy |
| Test restore | The only thing that proves a backup works |
Recovery sites
| Site | What is ready | Cost | Time to switch |
|---|---|---|---|
| Hot | Running systems and current data | Highest | Minutes |
| Warm | Hardware and connectivity, data needs restoring | Middle | Hours to a day |
| Cold | Space and power only | Lowest | Days to weeks |
| Cloud | Provisioned on demand | Pay as used | Minutes to hours |
Exams covered
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Three verified practice questions on this material. Answer one, and see the official page behind the answer.
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