IOPS是指单位时间内系统能处理的I/O请求数量，一般以每秒处理的I/O请求数量为单位。随机读写频繁的应用，如OLTP(Online Transaction Processing)，IOPS是关键衡量指标。
传统磁盘本质上是一种机械装置，转速通常为5400/7200/10K/15K rpm不等。磁盘完成一个I/O请求所花费的时间，由寻道时间、旋转延迟和数据传输时间三部分构成。寻道时间Tseek是指将磁头移动至正确的磁道上所需要的时间，其平均值一般在3~15ms。旋转延迟Trotation是指盘片旋转将请求数据所在扇区移至读写磁头下方所需要的时间，取决于磁盘转速，通常使用磁盘旋转一周所需时间的1/2表示，如，7200 rpm磁盘平均旋转延迟大约为60*1000/7200/2 = 4.17ms。数据传输时间Ttransfer是指传输所请求数据所需要的时间，它取决于数据传输率，目前IDE/ATA能达到133MB/s，SATA II可达到300MB/s的数据传输率。相对于寻道时间Tseek和旋转延迟Trotation，数据传输时间Ttransfer所占的比例往往是非常小的（取决于每次传输的数据量的大小，数据量大，则比例高，数据量小，则比例低）。
IOPS与读写负载特征息息相关。如果为顺序读写，则两次顺序读写之间的寻道时间和旋转时间可以忽略，因此顺序读写iops往往远大于随机读写iops。除此之外，iops也与存储的缓存、阵列的结构等有关。理论上可以计算出磁盘的最大随机IOPS，即IOPS = 1000 ms/ (Tseek + Troatation)，其值一般在100~200之间。
下面的图表非常清楚的表示了IOPS和读写特征的关系：(配置12块Maxtor 250GB, 7,200RPM的磁盘，512MB Cache)
在磁盘阵列系统中， 磁盘数量越多， IOPS 值越大 ( 几乎呈线性增长 )
而且在同样的配置下，IOPS值随磁盘中数据量的增加而下降
下面是常用磁盘的IOPS列表，参考自维基百科
| Device | Type | IOPS | Interface | Notes |
|---|---|---|---|---|
| 7,200 rpm SATA drives | HDD | ~75-100 IOPS[2] | SATA 3 Gbit/s | |
| 10,000 rpm SATA drives | HDD | ~125-150 IOPS[2] | SATA 3 Gbit/s | |
| 10,000 rpm SAS drives | HDD | ~140 IOPS[2] | SAS | |
| 15,000 rpm SAS drives | HDD | ~175-210 IOPS[2] | SAS |
Solid State Devices
| Device | Type | IOPS | Interface | Notes |
|---|---|---|---|---|
| Simple SLC SSD | SSD | ~400 IOPS[citation needed] | SATA 3 Gbit/s | |
| Intel X25-M G2(MLC) | SSD | ~8,600 IOPS[11] | SATA 3 Gbit/s | Intel's data sheet[12] claims 6,600/8,600 IOPS (80 GB/160 GB version) and 35,000 IOPS for random 4 KB writes and reads, respectively. |
| Intel X25-E(SLC) | SSD | ~5,000 IOPS[13] | SATA 3 Gbit/s | Intel's data sheet[14] claims 3,300 IOPS and 35,000 IOPS for writes and reads, respectively. 5,000 IOPS are measured for a mix. Intel X25-E G1 has around 3 times higher IOPS compared to the Intel X25-M G2.[15] |
| G.Skill Phoenix Pro | SSD | ~20,000 IOPS[16] | SATA 3 Gbit/s | SandForce-1200 based SSD drives with enhanced firmware, states up to 50,000 IOPS, but benchmarking shows for this particular drive ~25,000 IOPS for random read and ~15,000 IOPS for random write.[16] |
| OCZ Vertex 3 | SSD | Up to 60,000 IOPS[17] | SATA 6 Gbit/s | Random Write 4 KB (Aligned) |
| Corsair Force Series GT | SSD | Up to 85,000 IOPS[18] | SATA 6 Gbit/s | 240 GB Drive, 555 MB/s sequential read & 525 MB/s sequential write, Random Write 4 KB Test (Aligned) |
| OCZ Vertex 4 | SSD | Up to 120,000 IOPS[19] | SATA 6 Gbit/s | 256 GB Drive, 560 MB/s sequential read & 510 MB/s sequential write, Random Read 4 KB Test 90K IOPS, Random Write 4 KB Test 85K IOPS |
| Texas Memory Systems RamSan-20 | SSD | 120,000+ Random Read/Write IOPS[20] | PCIe | Includes RAM cache |
| Fusion-ioioDrive | SSD | 140,000 Read IOPS, 135,000 Write IOPS[21] | PCIe | |
| Virident SystemstachIOn | SSD | 320,000 sustained READ IOPS using 4KB blocks and 200,000 sustained WRITE IOPS using 4KB blocks[22] | PCIe | |
| OCZ RevoDrive 3 X2 | SSD | 200,000 Random Write 4K IOPS[23] | PCIe | |
| Fusion-io ioDrive Duo | SSD | 250,000+ IOPS[24] | PCIe | |
| Violin MemoryViolin 3200 | SSD | 250,000+ Random Read/Write IOPS[25] | PCIe /FC/Infiniband/iSCSI | Flash Memory Array |
| WHIPTAIL, ACCELA | SSD | 250,000/200,000+ Write/Read IOPS[26] | Fibre Channel, iSCSI, Infiniband/SRP, NFS, CIFS | Flash Based Storage Array |
| DDRdrive X1, | SSD | 300,000+ (512B Random Read IOPS) and 200,000+ (512B Random Write IOPS)[27][28][29][30] | PCIe | |
| SolidFireSF3010/SF6010 | SSD | 250,000 4KB Read/Write IOPS[31] | iSCSI | Flash Based Storage Array (5RU) |
| Texas Memory Systems RamSan-720 Appliance | SSD | 500,000 Optimal Read, 250,000 Optimal Write 4KB IOPS[32] | FC / InfiniBand | |
| OCZ Single SuperScale Z-Drive R4 PCI-Express SSD | SSD | Up to 500,000 IOPS[33] | PCIe | |
| WHIPTAIL,INVICTA | SSD | 650,000/550,000+ Read/Write IOPS[34] | Fibre Channel, iSCSI, Infiniband/SRP, NFS | Flash Based Storage Array |
| Violin MemoryViolin 6000 | 3RU Flash Memory Array | 1,000,000+ Random Read/Write IOPS[35] | /FC/Infiniband/10Gb(iSCSI)/ PCIe | |
| Texas Memory Systems RamSan-630 Appliance | SSD | 1,000,000+ 4KB Random Read/Write IOPS[36] | FC / InfiniBand | |
| Fusion-io ioDrive Octal (single PCI Express card) | SSD | 1,180,000+ Random Read/Write IOPS[37] | PCIe | |
| OCZ 2x SuperScale Z-Drive R4 PCI-Express SSD | SSD | Up to 1,200,000 IOPS[33] | PCIe | |
| Texas Memory Systems RamSan-70 | SSD | 1,200,000 Random Read/Write IOPS[38] | PCIe | Includes RAM cache |
| Kaminario K2 | Flash/DRAM/Hybrid SSD | Up to 1,200,000 IOPS SPC-1 IOPS with the K2-D (DRAM)[39][40] | FC | |
| Fusion-io ioDrive2 | SSD | Up to 9,608,000 IOPS[41] | PCIe |