Contract | Disk | RAID | MEMS | SSD |
1. Sequential accesses are much better than random accesses | T | T | T | F (flash memory, no mechanical parts) |
2. Distant LBNs lead to longer seek times | T * | F | T | F (log-structured writes) |
3. LBN spaces can be interchanged | F | F | T | F (integration of SLC and MLC memory) |
4. Data written is equal to data issued (no write amplification) | T | F | T | F (ganging, striping, larger logical pages) |
5. Media does not wear down | T | T | T | F (semiconductor properties) |
6. Storage devices are passive with little background activity | T * | F | T | F (cleaning and wear-leveling) |
Read | Write | |||||
Device | Seq | Rand | Ratio | Seq | Rand | Ratio |
HDD | 86.2 | 0.6 | 143.7 | 86.8 | 1.3 | 66.8 |
S1slc | 205.6 | 18.7 | 11.0 | 169.4 | 53.8 | 3.1 |
S2slc | 40.3 | 4.4 | 9.2 | 32.8 | 0.1 | 328.0 |
S3slc | 72.5 | 29.9 | 2.4 | 75.8 | 0.5 | 151.6 |
S4slc_sim | 30.5 | 29.1 | 1.1 | 24.4 | 18.4 | 1.3 |
S5mlc | 68.3 | 21.3 | 3.2 | 22.5 | 15.3 | 1.5 |
Probability of sequential access | 0 | 0.2 | 0.4 | 0.6 | 0.8 |
Unaligned | 10.6 | 10.6 | 10.5 | 10.2 | 10.5 |
Aligned | 10.6 | 10.4 | 8.9 | 7.6 | 5.6 |
Postmark | TPCC | Exchange | IOzone | |
Improvement (%) | 1.15 | 3.08 | 4.89 | 36.54 |
Transactions | 5000 | 6000 | 7000 | 8000 |
Relative pages moved | 0.31 | 0.25 | 0.35 | 0.50 |
Relative cleaning time | 0.69 | 0.60 | 0.63 | 0.69 |
Writes (%) | 20 | 40 | 50 | 60 | 80 |
Improvement (%) | 0 | 9.56 | 10.27 | 9.61 | 9.47 |