ssh / scp slow on 10GBE

Iain Morgan imorgan at
Tue Jan 8 05:59:12 EST 2013

On Sun, Jan 06, 2013 at 12:54:46 -0600, Stefan Priebe wrote:
> Hi Iain,
> Am 04.01.2013 20:08, schrieb Iain Morgan:
> >> openssl aes-128-cbc speed:
> >>
> >> The 'numbers' are in 1000s of bytes per second processed.
> >> type             16 bytes     64 bytes    256 bytes   1024 bytes   8192
> >> bytes
> >> aes-128-cbc     648664.33k   688924.90k   695855.45k   700784.64k 704027.06k
> >
> > As Tomas noted, the choice of MAC also impacts performance. The default
> > is hmac-md5, but umac-64 at can provide significantly better
> > performance.
> Oh i didn't saw tomas mail - maybe he just replied to the list. I'm not 
> subscribed. But i found his mail and will reply in a seperate email.
> I tried now umac-64 at this gives me 400MB/s - is this the 
> maximum i can expect through 10GBE? Link shows avg rate of 6,5Gbit/s.
> > I'm assuming that the number you quoted in your original email was from
> > an scp transfer. Be aware that it uses fairly coarse time granularity in
> > its calculations, so transfers of small files can report deceptive
> > values.
> Yes it was from scp but just transfering one 20GB file. But i missed the 
> disk speed problematic. In my original task i would just like to 
> transfer as much data as possible (in memory - no disks involved).
> Greets,
> Stefan

You may be able to further improve the performance by using aes128-ctr
instead of aes128-cbc. However, you will need to build OpenSSH from a
recent snapshot[1] to take advantage of this. You can find more details
in the list archive for December.

Iain Morgan


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