什么是USB3和USB2在SATA上的实际速度（stream，延迟）？

在配备Intel i7-4770K内存和Ubuntu 14.10的华硕Z87主板上，第一代英特尔80GB固态硬盘（X25-M）在ext4文件系统上使用了ioping实用程序，阅读performance的粗略估计：

SPEC: 250MB/sec, SATA: 240MB/sec, 1000 iops, 1ms latency USB3: 190MB/sec, 750 iops, 1.3ms latency USB2: 43MB/sec, 200 iops, 6ms latency 

当然，这对于不同的设置会有所不同。 这张表的目的是在非理论性的比较中增加一些延迟和iops统计。 下面的其余部分仅仅是上面的细节。

更多细节如下

 All Tests Run On An Intel 80GB First-Gen Drive, X25-M. Direct-Access ATA INTEL SSDSA2M080 02HA PQ: 0 ANSI: 5 Intel Posted X25-M Drive Specs: Read: 250MB/s Write: 70MB/s Latency Read: 65us Latency Write 85us IOPS: read=35k. write=300 to 6600 Motherboard: Asus Z87 Gryphon w/ USB 3.0 port. ---------------------------------------------------------------- on the SATA bus: # ioping -RL . --- . (ext4 /dev/sdb1) ioping statistics --- 2.8 k requests completed in 3.0 s, 952 iops, 238.0 MiB/s min/avg/max/mdev = 999 us / 1.1 ms / 2.1 ms / (85 us) # ioping -RL . --- . (ext4 /dev/sdb1) ioping statistics --- 2.8 k requests completed in 3.0 s, 956 iops, 239.2 MiB/s min/avg/max/mdev = 1.0 ms / 1.0 ms / 7.6 ms / (149 us) ---------------------------------------------------------------- on the USB 3.0 superspeed bus: Bus 003 Device 011: ID 152d:2509 JMicron Technology Corp. / JMicron USA Technology Corp. JMS539 SuperSpeed SATA II 3.0G Bridge # ioping -R . --- . (ext4 /dev/sdd1) ioping statistics --- 11.3 k requests completed in 3.0 s, 3.8 k iops, 14.8 MiB/s min/avg/max/mdev = 247 us / 264 us / 4.6 ms / (49 us) # ioping . 4.0 KiB from . (ext4 /dev/sdd1): request=1 time=1.6 ms 4.0 KiB from . (ext4 /dev/sdd1): request=2 time=333 us ... ^C --- . (ext4 /dev/sdd1) ioping statistics --- 12 requests completed in 11.5 s, 2.3 k iops, 9.1 MiB/s min/avg/max/mdev = 290 us / 427 us / 1.6 ms / (344 us) # ioping -RL . --- . (ext4 /dev/sdd1) ioping statistics --- 2.2 k requests completed in 3.0 s, 748 iops, 187.0 MiB/s min/avg/max/mdev = 1.3 ms / 1.3 ms / 3.6 ms / (96 us) ---------------------------------------------------------------- on the USB 2.0 high-speed bus: # ioping -R . --- . (ext4 /dev/sdd1) ioping statistics --- 509 requests completed in 3.0 s, 170 iops, 42.6 MiB/s min/avg/max/mdev = 5.8 ms / 5.9 ms / 6.3 ms / (67 us) # ioping -RL . --- . (ext4 /dev/sdd1) ioping statistics --- 510 requests completed in 3.0 s, 170 iops, 42.7 MiB/s min/avg/max/mdev = 5.8 ms / 5.9 ms / 6.3 ms / (42 us) ---------------------------------------------------------------- USB3 Bridge Device Bus 003 Device 011: ID 152d:2509 JMicron Technology Corp. / JMicron USA Technology Corp. JMS539 SuperSpeed SATA II 3.0G Bridge Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 2.10 bDeviceClass 0 (Defined at Interface level) bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 64 idVendor 0x152d JMicron Technology Corp. / JMicron USA Technology Corp. idProduct 0x2509 JMS539 SuperSpeed SATA II 3.0G Bridge bcdDevice 1.00 iManufacturer 1 JMicron iProduct 11 Usb production iSerial 3 00A123456A8D bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 32 bNumInterfaces 1 bConfigurationValue 1 iConfiguration 4 USB Mass Storage bmAttributes 0xc0 Self Powered MaxPower 2mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 2 bInterfaceClass 8 Mass Storage bInterfaceSubClass 6 SCSI bInterfaceProtocol 80 Bulk-Only iInterface 6 MSC Bulk-Only Transfer Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 2 Transfer Type Bulk Synch Type None Usage Type Data wMaxPacketSize 0x0200 1x 512 bytes bInterval 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x02 EP 2 OUT bmAttributes 2 Transfer Type Bulk Synch Type None Usage Type Data wMaxPacketSize 0x0200 1x 512 bytes bInterval 0 Binary Object Store Descriptor: bLength 5 bDescriptorType 15 wTotalLength 42 bNumDeviceCaps 3 USB 2.0 Extension Device Capability: bLength 7 bDescriptorType 16 bDevCapabilityType 2 bmAttributes 0x00000002 Link Power Management (LPM) Supported SuperSpeed USB Device Capability: bLength 10 bDescriptorType 16 bDevCapabilityType 3 bmAttributes 0x00 wSpeedsSupported 0x000e Device can operate at Full Speed (12Mbps) Device can operate at High Speed (480Mbps) Device can operate at SuperSpeed (5Gbps) bFunctionalitySupport 1 Lowest fully-functional device speed is Full Speed (12Mbps) bU1DevExitLat 10 micro seconds bU2DevExitLat 32 micro seconds Container ID Device Capability: bLength 20 bDescriptorType 16 bDevCapabilityType 4 bReserved 0 ContainerID {00010203-0405-0607-0800-000000000000} Device Status: 0x0001 Self Powered