Re: [rdiff-backup-users] rdiff-backup to LinkStation: *slow*

[Felix E. Klee]

At Fri, 26 May 2006 09:51:33 +0000 (GMT),
Chris Wilson wrote:
> > According to "top", the "ssh" server "dropbear" seems to be the limiting
> > factor.
> 
> You could try making sure that SSH compression is turned off as well. That 
> can eat quite a bit of CPU.

By default it should be off, but I tried again:

  $ time cat foo | \
  ssh -o Compression=no address@hidden "cat >/mnt/hda/share/sshtest.1/foo"
  address@hidden's password: 

  real    19m12.086s
  user    1m29.274s
  sys     0m21.933s

=> Almost no change in data rate, when compared to the test I did
without "-o Compression=no".

> You can also change the SSH encryption algorithm on the client host
> using the "Ciphers" option in /etc/ssh/ssh_config. According to this
> page, arcfour is faster [http://www.hlrn.de/doc/ssh/index.html]. See
> the man page for ssh_config for details.

The server (dropbear) does not support arcfour.  Only aes128-cbc,
blowfish-cbc, twofish-cbc, and 3des-cbc seem to be supported:

  $ time cat foo | ssh -o Compression=no -o Ciphers=arcfour \
  address@hidden "cat >/mnt/hda/share/sshtest.1/foo"
  no matching cipher found: client arcfour server 
aes128-cbc,blowfish-cbc,twofish-cbc,3des-cbc

  real    0m10.557s
  user    0m0.011s
  sys     0m0.009s

Of course I could try out those as well.  But speed is not the only
issue, security is also an issue.

> I don't think it's possible with rdiff-backup. You could try Box
> Backup, which does encrypt data on the client, and is intended to run
> on low-spec devices like the LinkStation. Currently it does encrypt
> the comms channel as well, but I'm sure the developers would be
> sympathetic to providing an option to disable this (I'm one of them).

Box Backup looks very interesting.

-- 
Felix E. Klee