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I have "Express Card USB 3.0 adapter" like this (it's in polish so I add to it Google translation, forgive that)

and I'm wondering what's wrong? Such adapters idea or my hardware, because I was copying a movie to USB 3.0 pendrive. Nautilus told me it was about 20MB/s.. . It's kinda slow for USB3.0, then I pluged the same pendrive to USB 2.0 and result was similar, like 20MB/s.

Why? Do I need a better driver or such adapters don't work? I use:

Linux ub-alef 3.8.0-22-generic #33-Ubuntu SMP Thu May 16 15:17:59 UTC 2013 i686 i686 i686 GNU/Linux
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The card is not PCI express, but Express Card. – Keltari May 28 '13 at 18:09
20MB/s is a respectable write speed for a USB 3.0 pendrive. Remember, every block may need to be erased before it can be written to. – David Schwartz May 28 '13 at 18:26
It sounds like the device in question is NOT a USB 3.0 device. The adapter clearly should be capable of faster transfer speeds. The product page does not indicate if its a USB 2.0 or USB 3.0 device. – Ramhound May 28 '13 at 19:04
It is. The product's wrapping has label 'super speed' + USBs are blue. – xliiv May 29 '13 at 6:48

That is an ExpressCard interface, which is not the same as PCI Express. The host side of the ExpressCard connector provides PCI Express lanes and USB pins. An ExpressCard-to-USB adapter often does nothing more than bring the USB data and power pins from the ExpressCard connector out to standard USB-A ports, possibly including a hub chip.

In that scenario, you'll get the same speed on the external ports as the internal USB pins had.

It's not clear whether your adapter actually has a PCIe -> USB bridge chip, or is merely a hub for the USB interface provided within ExpressCard.

The most likely scenario, however, is that you have a slow pendrive, or are copying from a slow source. Even USB 2.0 can get more than 20MB/s. Many "USB 3.0" pendrives have read speeds well above the USB 2.0 limit, but are still slow to write.

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I've got this pendrive:… It's write-50MB, read-100MB. Maybe file system difference cause that? I copied between NTFS(pendrive) and EXT4(HOST). – xliiv May 28 '13 at 18:47

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