1

What is the real-world speed (stream, latency) of USB3 and USB2 over SATA?

It is easy to find streaming speed comparisons, but more difficult to find latency comparisons in the same setup.

Answer to follow in a momemt.

2

On an ASUS Z87 motherboard with an intel i7-4770K with gobs of memory and ubuntu 14.10, the rough performance comparison of a first-gen Intel 80gb SSD drive (X25-M), using the ioping utility on an ext4 filesystem, the following is a rough estimate of read-performance:

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

Of course, this will be different for different setups. The point of this table was to add some latency and iops stats in a non-theoretical comparison. The rest below are merely details on the above.


More Details follow

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
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