SFTP (SSH) Performance

Discussion of the Co:Z Co-Processing Toolkit for z/OS
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dabills
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Joined: Thu May 19, 2011 9:56 am

SFTP (SSH) Performance

Post by dabills » Fri Jul 08, 2016 12:28 pm

I ran some tests between the mainframe and a zlinux server (Redhat 5) to compare pushing a file verses pulling a file. We are seeing about a 20% increase in CPU time used in SFTP/SSH when we pull a file from zlinux instead of pushing a file to zlinux. In both cases there was little to nothing else running on the LPAR we tested on so very little to no contention with other work.

I tried a couple different cipher algorithms, but in each case the pull always used more CPU resources. Is there anything I can do to make the pull use as much or less resources than the push. I am testing with the same file which is about 600MB doing a binary transfer.

dovetail
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Re: SFTP (SSH) Performance

Post by dovetail » Fri Jul 08, 2016 3:20 pm

Assuming that z/OS starts the connection, there will be two address spaces:

1) The JES batch address spaces, which will run COZBATCH, the Unix Shell, and the cozsftp command
2) The OMVS address space which will runs the IBM OpenSSH "/bin/ssh" program

The latter normally accounts for 90% of the CPU time. From your question it is unclear which you are concerned about.

Have you tuned IBM Ported Tools OpenSSH to exploit ICSF for crypto?
See the appropriate "Quick Install" guide for your release here: http://dovetail.com/docs/coz/coz_index.html
If you haven't done this, you can typically save 50% of the overall CPU time by following these steps.

If you are interested in additional assistance with tuning your system, you may wish to consider our Enterprise LIcense and Support agreements. Please send us an email at info@dovetai.com if you would like more information.

dabills
Posts: 41
Joined: Thu May 19, 2011 9:56 am

Re: SFTP (SSH) Performance

Post by dabills » Mon Jul 11, 2016 7:40 am

I'm more concerned when the mainframe is acting as the server when a Linux or UNIX box connects to it. We have already exploited ICSF for both the client and server SSH function. For some reason the SSHD uses more resources than the SSH.

dovetail
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Re: SFTP (SSH) Performance

Post by dovetail » Mon Jul 11, 2016 7:57 am

Perhaps your IBM SSHD is not properly configured for ICSF.
See "Verifying ICSF usage" in http://dovetail.com/docs/pt-quick-inst- ... lgs-server

dabills
Posts: 41
Joined: Thu May 19, 2011 9:56 am

Re: SFTP (SSH) Performance

Post by dabills » Tue Jul 12, 2016 8:00 am

SSHD is using ICSF. I confirmed that by looking at the DEBUG 3 logging messages produced by SSHD at connection time. Also, when we don't use ICSF, SSHD uses 50 - 60 percent more overhead using OpenSSH. I've also opened a ticket with IBM to see if they have any other ideas about SSHD overhead compared to SSH.

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