Comment # 5 on bug 1190539 from Michael Krapp

Ok, seems bad choice of hardware :-(

Bus 004 Device 003: ID 174c:55aa ASMedia Technology Inc. ASM1051E SATA 6Gb/s
bridge, ASM1053E SATA 6Gb/s bridge, ASM1153 SATA 3Gb/s bridge, ASM1153E SATA
6Gb/s bridge

It was the combination of Laptop Port, one of my cables and the external ssd
case

Same cable works with different external disk cases as well as the ASM1051E
with a different cable.


However, disabling uas for the above ASM1051E by booting with
"usb-storage.quirks=174c:55aa:u"  improves throughput by almost 50%

Example: 
Good cable WITH usb quirk:


kernel: usb 4-2: new SuperSpeed USB device number 5 using xhci_hcd
kernel: usb 4-2: New USB device found, idVendor=174c, idProduct=55aa,
bcdDevice= 1.00
kernel: usb 4-2: New USB device strings: Mfr=2, Product=3, SerialNumber=1
kernel: usb 4-2: Product: ASM105x
kernel: usb 4-2: Manufacturer: ASMT
kernel: usb 4-2: SerialNumber: ACDFD0000000000007B4
kernel: usb 4-2: UAS is ignored for this device, using usb-storage instead
kernel: usb-storage 4-2:1.0: USB Mass Storage device detected
kernel: usb-storage 4-2:1.0: Quirks match for vid 174c pid 55aa: c00000
kernel: scsi host0: usb-storage 4-2:1.0

> sudo dd if=/dev/sda of=/dev/null status=progress
2423468032 bytes (2.4 GB, 2.3 GiB) copied, 7 s, 346 MB/s


WithOUT quirks:

kernel: usb 4-2: new SuperSpeed USB device number 6 using xhci_hcd
 kernel: usb 4-2: New USB device found, idVendor=174c, idProduct=55aa,
bcdDevice= 1.00
 kernel: usb 4-2: New USB device strings: Mfr=2, Product=3, SerialNumber=1
 kernel: usb 4-2: Product: ASM105x
 kernel: usb 4-2: Manufacturer: ASMT
 kernel: usb 4-2: SerialNumber: ACDFD0000000000007B4
 kernel: usbcore: registered new interface driver usb-storage 
 kernel: scsi host0: uas
 kernel: usbcore: registered new interface driver uas
 kernel: scsi 0:0:0:0: Direct-Access     ASMT     2115             0    PQ: 0
ANSI: 6           
 kernel: scsi 0:0:0:0: Attached scsi generic sg0 type 0
 kernel: sd 0:0:0:0: [sda] 937721856 512-byte logical blocks: (480 GB/447 GiB)
 kernel: sd 0:0:0:0: [sda] Write Protect is off
 kernel: sd 0:0:0:0: [sda] Mode Sense: 43 00 00 00
 kernel: sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't
support DPO or FUA
 kernel: sd 0:0:0:0: [sda] Optimal transfer size 33553920 bytes 
 kernel:  sda: sda1
 kernel: sd 0:0:0:0: [sda] Attached SCSI disk


> sudo dd if=/dev/sda of=/dev/null status=progress
1674818048 bytes (1.7 GB, 1.6 GiB) copied, 7 s, 238 MB/s


So, with quirks set (disable uas for this device) I get 346 MB/s reading from
device, without quirk, throughput is only 238 MB/s


I will definitely look for another ssd case :)