Model
Scrubbing: bandwidth and the detection window
Retention depth is not only a recovery-window decision. It is also a detection-lag decision.
- Scrub cycle
- time to read every stored block once
- Retention
- how long backups keep a good copy
How it behaves
One input on the horizontal axis, the others held fixed.
Data table
| Data stored | Scrub read rate (bytes/s) |
|---|---|
| 931 GB | 377 KB |
| 1.05 TB | 435 KB |
| 1.21 TB | 502 KB |
| 1.4 TB | 580 KB |
| 1.62 TB | 670 KB |
| 1.87 TB | 774 KB |
| 2.16 TB | 893 KB |
| 2.49 TB | 1.01 MB |
| 2.88 TB | 1.16 MB |
| 3.32 TB | 1.34 MB |
| 3.84 TB | 1.55 MB |
| 4.43 TB | 1.79 MB |
| 5.11 TB | 2.07 MB |
| 5.91 TB | 2.39 MB |
| 6.82 TB | 2.76 MB |
| 7.88 TB | 3.19 MB |
| 9.09 TB | 3.68 MB |
| 10.5 TB | 4.25 MB |
| 12.1 TB | 4.91 MB |
| 14 TB | 5.67 MB |
| 16.2 TB | 6.54 MB |
| 18.7 TB | 7.56 MB |
| 21.6 TB | 8.72 MB |
| 24.9 TB | 10.1 MB |
| 28.8 TB | 11.6 MB |
| 33.2 TB | 13.4 MB |
| 38.4 TB | 15.5 MB |
| 44.3 TB | 17.9 MB |
| 51.1 TB | 20.7 MB |
| 59.1 TB | 23.9 MB |
| 68.2 TB | 27.6 MB |
| 78.8 TB | 31.9 MB |
| 90.9 TB | 36.8 MB |
| 105 TB | 42.5 MB |
| 121 TB | 49.1 MB |
| 140 TB | 56.7 MB |
| 162 TB | 65.4 MB |
| 187 TB | 75.6 MB |
| 216 TB | 87.2 MB |
| 249 TB | 101 MB |
| 288 TB | 116 MB |
| 332 TB | 134 MB |
| 384 TB | 155 MB |
| 443 TB | 179 MB |
| 511 TB | 207 MB |
| 591 TB | 239 MB |
| 682 TB | 276 MB |
| 788 TB | 319 MB |
| 909 TB | 368 MB |
| 1,050 TB | 425 MB |
| 1,210 TB | 491 MB |
| 1,400 TB | 567 MB |
| 1,620 TB | 654 MB |
| 1,870 TB | 756 MB |
| 2,160 TB | 872 MB |
| 2,490 TB | 1,010 MB |
| 2,880 TB | 1.14 GB |
| 3,320 TB | 1.31 GB |
| 3,840 TB | 1.52 GB |
| 4,430 TB | 1.75 GB |
| 5,110 TB | 2.02 GB |
| 5,910 TB | 2.33 GB |
| 6,820 TB | 2.69 GB |
| 7,880 TB | 3.11 GB |
| 9,090 TB | 3.59 GB |
| 10,500 TB | 4.15 GB |
| 12,100 TB | 4.79 GB |
| 14,000 TB | 5.53 GB |
| 16,200 TB | 6.39 GB |
| 18,700 TB | 7.38 GB |
| 21,600 TB | 8.52 GB |
| 24,900 TB | 9.84 GB |
| 28,800 TB | 11.4 GB |
| 33,200 TB | 13.1 GB |
| 38,400 TB | 15.2 GB |
| 44,300 TB | 17.5 GB |
| 51,100 TB | 20.2 GB |
| 59,100 TB | 23.3 GB |
| 68,200 TB | 26.9 GB |
| 78,800 TB | 31.1 GB |
| 90,900 TB | 35.9 GB |
Worked examples, recomputed
Every number the mechanisms quote for this relationship is recomputed from it, so none of them disagrees with it.
Where it appears
Each mechanism states it in its own names. The general symbol each name stands for is shown with it.
- Persistence & Durability
When a system says "yes, your data is safe", what exactly has it promised, and what did it have to do to keep that promise?