硬盘IOPS[fn:3][fn:4]

| size | RPM | Seek time | Avg Rota latency | Throught | Random IOPS | | | | | 0.5/(RPM/60) | | 1/(seek+latency) | |——+——-+———–+——————+———-+——————| | 2.5 | 15000 | 4ms | 2ms | 6Gbps | ~175-210 | | 2.5 | 10000 | 4ms | 3ms | 6Gbps | ~175-210 | | 3.5 | 15000 | 8ms | 2ms | 6Gbps | ~140 | | 3.5 | 10000 | 8ms | 3ms | 6Gbps | ~140 | | 2.5 | 7200 | 10ms | 4ms | 3Gbps | ~75-100 | | | | | | | |

RAID对IOPS影响[fn:1][fn:2][fn:6]

| RAID Level | Read | write | |————+——+——-| | 0 | 1 | 1 | | 1 / 10 | 1 | 2 | | 5 | 1 | 4 | | 6 | 1 | 6 | 参照上表，一个raid6的存储，一个写请求需要消耗6个IOPS，简单计算一下，如果你需要一个250IOPS的存储，一半读一半写，那就意味着你需要准备(250*50% + 250*50%*6)=875 的IOPS存储。

Latency comparison[fn:5]

L1 cache reference                            0.5 ns
Branch mispredict                             5   ns
L2 cache reference                            7   ns             14x L1 cache
Mutex lock/unlock                            25   ns
Main memory reference                       100   ns             20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy              3,000   ns
Send 1K bytes over 1 Gbps network        10,000   ns    0.01 ms
Read 4K randomly from SSD*              150,000   ns    0.15 ms
Read 1 MB sequentially from memory      250,000   ns    0.25 ms
Round trip within same datacenter       500,000   ns    0.5  ms
Read 1 MB sequentially from SSD*      1,000,000   ns    1    ms  4X memory
Disk seek                            10,000,000   ns   10    ms  20x datacenter roundtrip
Read 1 MB sequentially from disk     20,000,000   ns   20    ms  80x memory, 20X SSD
Send packet CA->Netherlands->CA     150,000,000   ns  150    ms