Date: Thu, 25 Jan 2007 23:12:38 -0700 From: Scott Long <scottl@samsco.org> To: "M. Warner Losh" <imp@bsdimp.com> Cc: current@freebsd.org Subject: Re: Interesting speed benchmarks Message-ID: <45B99BD6.3000709@samsco.org> In-Reply-To: <20070125.192448.-432840241.imp@bsdimp.com> References: <20070125.192448.-432840241.imp@bsdimp.com>
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M. Warner Losh wrote: > On a lark, I just got a combo USB/Firewire external disk drive. I ran > some crude benchmarks, and I was surprised by what I found. This is > on a fairly stock -current kernel. > > Firewire does around 40MB/s, while USB 2.0 maxes out at about 12MB/s. > This is with a simple dd command: > > When the enclosure was attached as firewire, I got these numbers: > > dd if=/dev/da0 of=/dev/null bs=1m count=1000 > 1048576000 bytes transferred in 25.867655 secs (40536183 bytes/sec) > 1048576000 bytes transferred in 25.886887 secs (40506068 bytes/sec) > 1048576000 bytes transferred in 25.880712 secs (40515733 bytes/sec) > > when it was attached via usb (same disk): > dd if=/dev/da1 of=/dev/null bs=1m count=1000 > 1048576000 bytes transferred in 91.098764 secs (11510321 bytes/sec) > <gave up waiting for other runs> > > and for comparison (apples to oranges, I know): > > dd if=/dev/ad0 of=/dev/null bs=1m count=1000 > 1048576000 bytes transferred in 32.173160 secs (32591639 bytes/sec) > 1048576000 bytes transferred in 32.139310 secs (32625965 bytes/sec) > 1048576000 bytes transferred in 32.114549 secs (32651120 bytes/sec) > > Summary: > > firewire 40.5 MB/s Pretty much the speed I would expect. Yeah, it's not 50MB/s, but the firewire stack is under Giant so it's adding latency that is probably not optimal for getting the disk to cluster the reads. > usb 11.5 MB/s umass still bounces all I/O through a local buffer, right? That'll add a lot of latency, on top of the Giant-induced latency. > ata 32.6 MB/s Laptop drives are notoriously slow. This is a 4200RPM drive, while your firewire and USB drives are probably 5400 or 7200 RPM. It's also 2.5", so it has a smaller average linear velocity under the heads than a 3.5" drive. > > So why the huge difference? This is all the more amaizing because > 400Mb/s is 50MB/s.[*] > > Warner > > P.S. This is on my amd64 laptop, which may be why ata didn't do so > well. amd64 will only give a penalty to ATA if you have more than 4GB of RAM. Scott
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