COZBATCH transmission time fluctuates wildly.

Discussion of Co:Z sftp, a port of OpenSSH sftp for z/OS
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ts01spd
Posts: 6
Joined: Wed Jan 05, 2011 6:24 pm
Location: Denver, CO

COZBATCH transmission time fluctuates wildly.

Post by ts01spd »

Hello, I'm hoping y'all might have a suggestion where I may look or have heard of something similar.

We have some large transmissions from z/OS to UNIX where the total time to transmit fluctuates dramatically.
For example, there is a 264GB file that usually takes 8-9 hours but I've seen it go as fast as 3 hours and as long as 14.

I don't see any issues in Network traces (retransmissions or other issues) - The traces are huge so it is not easy but that is what I believe I see.
- It looks like z/OS is just not sending as fast as it can but my gut says the remote is telling us to slow down (but not using window size).
The performance tech sees no delays or constraints on the Source z/OS Mainframe.
I don't believe the destination has looked much yet (they want us to prove it of course).

I added -vvv to see if that added any information but not any that I can see.
Following is an example block that basically just repeats over and over on a faster or a slower transmission.

debug3: SSH2_FXP_STATUS 0
debug3: In write loop, ack for 220 32768 bytes at 7045120
debug3: Sent message SSH2_FXP_WRITE I:285 O:9175040 S:32768
debug3: SSH2_FXP_STATUS 0
debug3: In write loop, ack for 221 32768 bytes at 7077888
debug3: Sent message SSH2_FXP_WRITE I:286 O:9207808 S:32768
debug3: SSH2_FXP_STATUS 0
debug3: In write loop, ack for 222 32768 bytes at 7110656
debug3: Sent message SSH2_FXP_WRITE I:287 O:9240576 S:32768
debug3: SSH2_FXP_STATUS 0
debug3: In write loop, ack for 223 32768 bytes at 7143424
debug3: Sent message SSH2_FXP_WRITE I:288 O:9273344 S:32768
hannel 0: rcvd adjust 131072

Might there be some other debug I might do under PGM=COZBATCH that could shed some light on this?
dovetail
Site Admin
Posts: 2019
Joined: Thu Jul 29, 2004 12:12 pm

Re: COZBATCH transmission time fluctuates wildly.

Post by dovetail »

Co:Z SFTP uses IBM z/OS OpenSSH for it's low level network connection.

If you are having delays, there are almost certainly either:

1) in the network or remote server. Have a network engineer check with a tool like wireshark
2) lack of resources (CPU) given to /bin/ssh or sshd by WLM
ts01spd
Posts: 6
Joined: Wed Jan 05, 2011 6:24 pm
Location: Denver, CO

Re: COZBATCH transmission time fluctuates wildly.

Post by ts01spd »

Thanks for the reply.

Therein lies the issue.
- I and several other people including our top level people that look at traces and looked at several wireshark traces and see no "Network" issue.
- The remote has looked at their side (I heard today) and sees nothing
- The z/OS performance group has looked and sees no delays or resource constraints of any kind.

That was why I asked if you knew of any other debugging I might do to see if the remote is telling us to slow down in the SFTP Packet (rather than with the Window size).

Since we've still found nothing beyond it appears z/OS is not sending as fast as it can I'll open a ticket with IBM as well - Maybe they have a suggestion.
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