topic Re: Can ssh version make impact on the scp traffic in Operating System - Linux

Can ssh version make impact on the scp traffic

skt_skt — Fri, 13 Jul 2007 15:24:33 GMT

the OS on both source and destination are
Red Hat Linux Advanced Server release 2.1AS.
Can ssh version make impact on the scp traffic?(LAN traffic)

Another scenario if the same servers pass the data through WAN link(35mbps); what UNIX commands can trasfer data in a better speed.Currently my scp command take more than 24 Hours to copy 50GB data.

Re: Can ssh version make impact on the scp traffic

Victor Semaska_3 — Fri, 13 Jul 2007 15:49:10 GMT

If my math is OK that's about 606 KB/sec which is very slow.

Haven't heard of different ssh versions affecting speed. Things to check:

What speed are the NICs set to? I have seen some Linux systems set the NICs to 10 Mb/sec for some reason. Check with mii-tool.

scp encrypts/decrypts the data which is CPU intensive. Are the CPUs busy doing other work? Check with top.

If you allow ftp, try a ftp transfer to see if that's much faster. ftp doesn't encrypt the data.

Not that familiar with this area but I've had problems when the network switches are set up to match your servers. Talk to whoever manages your network.

Vic

Re: Can ssh version make impact on the scp traffic

skt_skt — Fri, 13 Jul 2007 15:56:14 GMT

Interms on speed i am looking for suggetion on a WAN scenario..

LAN scenario, my question would be if a lower ssh version can a difference in the data trasnfer speed?I have same ssh version on both source and dest hosts.

Re: Can ssh version make impact on the scp traffic

Stuart Browne — Fri, 13 Jul 2007 16:13:06 GMT

There are flaws in some of the older versions of SSH which affect the transfer speeds, so it's always a good idea to make sure they are up-to-date, but having different source/dest versions shouldn't make a difference (assuming neither have such bugs).

I'm going to assume that neither the source nor dest are CPU bound, so the encryption isn't causing the issue (using a lighter encryption method (BlowFish for example) would be a good test for that). .. (Besides, Victor already asked).

You're not imposing any speed limits in any QoS or Firewalls between the two boxes? And are not using the '-l' (limit speed) flag anywhere ?

I guess there is also the question of local link congestion (at either end). The WAN isn't already congested with other traffic?

Have you tried changing the 'Compression' setting?

Re: Can ssh version make impact on the scp traffic

skt_skt — Fri, 13 Jul 2007 16:38:37 GMT

How can i change the encryptiuon method?
WAN traffic is a static part and want to be as it is.

How can i change the compression setting?

Re: Can ssh version make impact on the scp traffic

Vitaly Karasik_1 — Sun, 15 Jul 2007 00:57:32 GMT

Before tweaking ssh settings I'll suggest you to compare scp speed with ftp/rcp transfer.

Re: Can ssh version make impact on the scp traffic

Stuart Browne — Sun, 15 Jul 2007 01:15:48 GMT

The option:

Compression yes

in your '/etc/ssh/sshd_options' to turn it on globally.

For a particular instance, you can use:

-C -o 'CompressionLevel 9'

The 'CompressionLevel' is the value to use against zlib, i.e. 'gzip -9'. To change the cipher, use:

-c blowfish

or some other cipher. See 'man ssh_config' for all the availables.

Re: Can ssh version make impact on the scp traffic

skt_skt — Sun, 15 Jul 2007 10:49:50 GMT

Hereis comparison result and there is almost 50% improvement reported at this moment. (Just to remind it may depend on the WAN traffic at that moment).

test yourself if any one feel this is appropriate to you and post the result.

# scp -p /var/log/messages xx:/yy/.
messages 100% |**************************************************************************| 676 MB 18:09

# scp -C -c blowfish -oCompressionLevel=9 -p /var/log/messages xx:/yy/.
messages 100% |**************************************************************************| 676 MB 07:36

I will test it further on different time.Hope it worked.

Re: Can ssh version make impact on the scp traffic

skt_skt — Sun, 15 Jul 2007 10:53:20 GMT

I will assign 3 more points to make a total of 10

Re: Can ssh version make impact on the scp traffic

Al Licause — Wed, 18 Jul 2007 08:08:30 GMT

Take a look at this article:

http://www.psc.edu/networking/projects/hpn-ssh/

It will explain some of the issues around
throughput with scp vs something like ftp.

By default ssh is self limiting and will always
be slower than ftp. It's really not an issue
of encryption but buffering.

Re: Can ssh version make impact on the scp traffic

skt_skt — Thu, 19 Jul 2007 21:25:16 GMT

The intention of this question was to improve the scp efficiency, even though the question is a little different. But i got a solution