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Date: Mon, 2 Jan 2017 20:39:30 +1100 (EST)
From: Ian Smith <smithi@nimnet.asn.au>
To: "Marat N.Afanasyev" <amarat@li.ru>
cc: FreeBSD stable <freebsd-stable@freebsd.org>
Subject: Re: usb 3.0 thumb drive speed limit
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On Mon, 2 Jan 2017 11:27:49 +0300, Marat N.Afanasyev wrote:
 > I wonder is there a speed limit on usb 3.0? I've bought
 > 
 > ugen0.4: <SanDisk> at usbus0
 > umass2 on uhub7
 > umass2: <SanDisk Extreme, class 0/0, rev 2.10/0.10, addr 4> on usbus0
 > da2 at umass-sim2 bus 2 scbus9 target 0 lun 0
 > da2: <SanDisk Extreme 0001> Removable Direct Access SPC-4 SCSI device
 > da2: Serial Number AA010808161609220143
 > da2: 40.000MB/s transfers
 > da2: 59840MB (122552320 512 byte sectors)
 > da2: quirks=0x2<NO_6_BYTE>
 > 
 > that claims 'Up to 245 MBytes/sec read speed'
 > 
 > and dd shows:
 > 
 > % dd if=/dev/da2 of=/dev/null bs=1m count=1000
 > 1000+0 records in
 > 1000+0 records out
 > 1048576000 bytes transferred in 25.688997 secs (40818098 bytes/sec)
 > 
 > why we have such a limit?

Seems you've plugged it into a USB 2 port, not USB 3

At least you're getting full USB 2 performance (40MB/s)

Check if you have one or more USB 3 ports with 'dmesg | grep xhci'

cheers, Ian