Exadata Rack Disk Type Disk Count Disk Model IOPS FULL（1/1） HP 14*12=168 15000rpm SAS 600G 50000 HC 7200rpm SAS 3T 28000 HALF（1/2） HP 7*12=68 15000rpm SAS 600G 25000 HC 7200rpm SAS 3T 14000 QUAR（1/4） HP 3*12=36 15000rpm SAS 600G 10800 HC 7200rpm SAS 3T 6000

IOPS在75-100, 我们取这个区间的最大值重新计算1/4 HC的总的IOPS只有3600, 相比官方宣称的6000少了40%。同样实际计算出来的HP也将近少了33%。为什么会存在如此大的差异？难道这个数值不准？那么同样我们使用另外一种计算方式来得到IOPS，以下采用一种比较流传甚光的方式来计算硬盘的IOPS：IOPS（每秒IO次数） = 1s/(寻道时间+旋转延迟+数据传输时间)

IOPS（7200rpm）= 1000 / (3 + 60000/7200/2) = 140
IOPS (10000rpm) = 1000 / (3 + 60000/10000/2) = 167
IOPS (15000rpm)= 1000 / (3 + 60000/15000/2) = 200

```INFO: Running /usr/local/bin/dcli -g /opt/oracle.SupportTools/onecommand/cell_group -l root cellcli -e calibrate force to calibrate cells...
SUCCESS: Ran /usr/local/bin/dcli -g /opt/oracle.SupportTools/onecommand/cell_group -l root cellcli -e calibrate force and it returned: RC=0
cel01: Calibration will take a few minutes...
cel01: Aggregate random read throughput across all hard disk luns: 1466 MBPS
cel01: Aggregate random read throughput across all flash disk luns: 4183.67 MBPS
cel01: Aggregate random read IOs per second (IOPS) across all hard disk luns: 2369
cel01: Aggregate random read IOs per second (IOPS) across all flash disk luns: 157585
cel01: Controller read throughput: 2020.61 MBPS
cel01: Calibrating hard disks  ...(read only)
cel01: Lun 0_0  on drive [20:0     ] random read throughput: 126.08 MBPS, and 194 IOPS
cel01: Lun 0_1  on drive [20:1     ] random read throughput: 122.98 MBPS, and 190 IOPS
cel01: Lun 0_10 on drive [20:10    ] random read throughput: 132.91 MBPS, and 200 IOPS
cel01: Lun 0_11 on drive [20:11    ] random read throughput: 126.68 MBPS, and 199 IOPS
cel01: Lun 0_2  on drive [20:2     ] random read throughput: 132.73 MBPS, and 204 IOPS
cel01: Lun 0_3  on drive [20:3     ] random read throughput: 126.32 MBPS, and 201 IOPS
cel01: Lun 0_4  on drive [20:4     ] random read throughput: 131.33 MBPS, and 202 IOPS
cel01: Lun 0_5  on drive [20:5     ] random read throughput: 129.67 MBPS, and 202 IOPS
cel01: Lun 0_6  on drive [20:6     ] random read throughput: 131.65 MBPS, and 201 IOPS
cel01: Lun 0_7  on drive [20:7     ] random read throughput: 127.67 MBPS, and 200 IOPS
cel01: Lun 0_8  on drive [20:8     ] random read throughput: 127.63 MBPS, and 201 IOPS
cel01: Lun 0_9  on drive [20:9     ] random read throughput: 130.88 MBPS, and 201 IOPS
cel01: Calibrating flash disks (read only, note that writes will be significantly slower) ...
cel01: Lun 1_0  on drive [FLASH_1_0] random read throughput: 273.71 MBPS, and 20013 IOPS
cel01: Lun 1_1  on drive [FLASH_1_1] random read throughput: 272.84 MBPS, and 20014 IOPS
cel01: Lun 1_2  on drive [FLASH_1_2] random read throughput: 272.78 MBPS, and 19996 IOPS
cel01: Lun 1_3  on drive [FLASH_1_3] random read throughput: 273.64 MBPS, and 19962 IOPS
cel01: Lun 2_0  on drive [FLASH_2_0] random read throughput: 273.73 MBPS, and 20738 IOPS
cel01: Lun 2_1  on drive [FLASH_2_1] random read throughput: 273.81 MBPS, and 20724 IOPS
cel01: Lun 2_2  on drive [FLASH_2_2] random read throughput: 273.69 MBPS, and 20734 IOPS
cel01: Lun 2_3  on drive [FLASH_2_3] random read throughput: 273.96 MBPS, and 20737 IOPS
cel01: Lun 4_0  on drive [FLASH_4_0] random read throughput: 273.63 MBPS, and 19959 IOPS
cel01: Lun 4_1  on drive [FLASH_4_1] random read throughput: 273.85 MBPS, and 19933 IOPS
cel01: Lun 4_2  on drive [FLASH_4_2] random read throughput: 273.76 MBPS, and 19944 IOPS
cel01: Lun 4_3  on drive [FLASH_4_3] random read throughput: 272.97 MBPS, and 19911 IOPS
cel01: Lun 5_0  on drive [FLASH_5_0] random read throughput: 273.87 MBPS, and 20022 IOPS
cel01: Lun 5_1  on drive [FLASH_5_1] random read throughput: 273.04 MBPS, and 20002 IOPS
cel01: Lun 5_2  on drive [FLASH_5_2] random read throughput: 273.66 MBPS, and 19998 IOPS
cel01: Lun 5_3  on drive [FLASH_5_3] random read throughput: 273.77 MBPS, and 19991 IOPS
cel01: CALIBRATE results are within an acceptable range.```

600G 1500rpm HP disk：Seagate ST3600057SS， Hitachi HUS156060VLS600
3T 7200rpm HC disk： Seagate ST33000650SS
2T 7200rpm HC disk： Seagate ST32000444SS， Hitachi HUS723020ALS640

Tool for Gathering I/O Resource Manager Metrics: metric_iorm.pl (Doc ID 1337265.1)

1. 这里提供的IOPS是一个最大值，也就是maximum value， 也就是说这个IOPS只是一个瞬间的极值，通常只能维持较短的时间，而不是能够一直保持的。
2. Others quote IOPS based on 2K, 4K or smaller IOs and are not relevant for databases 这句话显然是有问题的。尽管数据库块大小是8192字节，但是在Linux的OS blocksize是4096字节, Solaris的OS blocksize是512字节， 也就是说大于4096字节和512字节的块在操作系统层面是不识别的，最终是将数据库的块进行分拆，所以这里说2k， 4k的IO与database不相关显然是不准确的。另外磁盘的最小的读写单位是扇区，而绝大多数磁盘的扇区大小是4096字节。参看http://www.ibm.com/developerworks/linux/library/l-4kb-sector-disks/ ， 所以这里说的无关是不准确的。
3. 绝大多数的IOPS测试是基于4k的， 同样的F20的flash卡是提供4k随机读写的IOPS的指标的，为什么硬盘不能提供这个指标？