Re: Linux-Netbsd huge difference of speed, same hardware

[Andreas Kusalananda Kähäri <andreas.kahari%nbis.se@localhost>]

On Wed, Mar 04, 2020 at 10:07:29AM +0100, Pierre Dupond wrote:
> Thanks for the tip. It is a little bit faster now
> but still much less fast than  with Linux. Why the use
> of the raw device makes a difference.
> 
> The transcript of the commands when using
> the raw device is:
> 
> oche# dd if=/dev/urandom of=/dev/rld0f bs=32k count=1000
> 1000+0 records in
> 1000+0 records out
> 32768000 bytes transferred in 7.726 secs (4241263 bytes/sec)
> oche# dd if=/dev/urandom of=/dev/rld0f bs=32k count=10000
> 10000+0 records in
> 10000+0 records out
> 327680000 bytes transferred in 90.755 secs (3610599 bytes/sec)
> oche# ^C
> oche# dd if=/dev/urandom of=/dev/rld0f bs=2m count=100
> 100+0 records in
> 100+0 records out
> 209715200 bytes transferred in 45.064 secs (4653719 bytes/sec)


Are you using the same implementation of dd(1) on both systems?  As was
previously mentioned, GNU dd may return before all data has actually
been written to disk.  Also, it's not clear whether you're actually
testing the speed of the /dev/urandom device here.  Maybe use a more
neutral device such as /dev/zero or a static file?

In the end, if Linux seems to be faster and better for doing what you
need to do, then maybe do that thing on Linux?


> 
> Le 04.03.20 à 08:20, Martin Husemann a écrit :
> > On Wed, Mar 04, 2020 at 08:08:34AM +0100, Pierre Dupond wrote:
> >> I try to execute the command "dd if=/dev/urandom of=/dev/ld0f bs=2m" (or "bs=32k" but
> >> this make no difference).
> >
> > You want of=/dev/rld0f here.
> >
> > Also I dimly remember gnu dd not flushing the output or something unless
> > some special option is given, but that should not make a real difference for
> > huge transfers.
> >
> > Martin
> >

-- 
Andreas (Kusalananda) Kähäri
SciLifeLab, NBIS, ICM
Uppsala University, Sweden