Discussion:
FTP performance problem.
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Gadi Ben-Avi
2018-06-06 12:14:50 UTC
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Hi,

I have the following problem.
I need to transfer a very large file (3.7 GB) from a ftp server to z/OS.

First, I tried transferring the file using the z/OS ftp client. It took forever, and then timed out. The average transfer rate was somewhere between 500 and 100 KB/sec.
The transfer kept abending.

I transferred the file to my pc. That took about 10 minutes. The transfer rate was about 5 MB/sec.
I next transferred the file to z/OS using the windows ftp client and the z/OS ftp server. It took 71 seconds.

Where should I look to find the problem?

We are running z/OS v2.2

Gadi

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Rob Schramm
2018-06-06 12:19:53 UTC
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I am most interested in the abend.

Rob Schramm
Post by Gadi Ben-Avi
Hi,
I have the following problem.
I need to transfer a very large file (3.7 GB) from a ftp server to z/OS.
First, I tried transferring the file using the z/OS ftp client. It took
forever, and then timed out. The average transfer rate was somewhere
between 500 and 100 KB/sec.
The transfer kept abending.
I transferred the file to my pc. That took about 10 minutes. The transfer
rate was about 5 MB/sec.
I next transferred the file to z/OS using the windows ftp client and the
z/OS ftp server. It took 71 seconds.
Where should I look to find the problem?
We are running z/OS v2.2
Gadi
????? ?? ????? ???? ???? ???? ?????? ??? ??? ?????? ???? ????? ??? ??????
??????. ?? ????, ???????? ?? ??? ???? ?????, ??????? ???? ???? ????? ?? ???
????? ?????? ?? ?????. ????? ????? ???? ?? ?????? ?????? ?????? ???? ??
???? ??????? ??? ???, ?/?? ?????, ????? ?? ????? ????? ????? ????? ??????
?? ????? ??????? ?/?? ?????? ?? ??????.
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Rob Schramm

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Gadi Ben-Avi
2018-06-06 12:26:17 UTC
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The messages I see are:
EZA1475I Connection with 10.206.1.46 terminated
EZA1735I Std Return Code = 16150, Error Code = 00010

The job doesn't abend, but ends with condition code 3862

-----Original Message-----
From: IBM Mainframe Discussion List <IBM-***@LISTSERV.UA.EDU> On Behalf Of Rob Schramm
Sent: Wednesday, June 6, 2018 3:20 PM
To: IBM-***@LISTSERV.UA.EDU
Subject: Re: FTP performance problem.

I am most interested in the abend.

Rob Schramm
Post by Gadi Ben-Avi
Hi,
I have the following problem.
I need to transfer a very large file (3.7 GB) from a ftp server to z/OS.
First, I tried transferring the file using the z/OS ftp client. It
took forever, and then timed out. The average transfer rate was
somewhere between 500 and 100 KB/sec.
The transfer kept abending.
I transferred the file to my pc. That took about 10 minutes. The
transfer rate was about 5 MB/sec.
I next transferred the file to z/OS using the windows ftp client and
the z/OS ftp server. It took 71 seconds.
Where should I look to find the problem?
We are running z/OS v2.2
Gadi
????? ?? ????? ???? ???? ???? ?????? ??? ??? ?????? ???? ????? ??? ??????
??????. ?? ????, ???????? ?? ??? ???? ?????, ??????? ???? ???? ????? ?? ???
????? ?????? ?? ?????. ????? ????? ???? ?? ?????? ?????? ?????? ???? ??
???? ??????? ??? ???, ?/?? ?????, ????? ?? ????? ????? ????? ????? ??????
?? ????? ??????? ?/?? ?????? ?? ??????.
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Rob Schramm

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הודעה זו נשלחה אליך מטעם חברה בקבוצת מלם תים וייתכן שהיא מוגנת תחת סודיות מסחרית. כל הצעה, התחייבות או מצג מטעם החברה, מחייבים מסמך נפרד וחתום על ידי מורשה החתימה של החברה. החברה רשאית לנטר כל תכתובת העוברת בשרתיה והיא לא תישא באחריות לכל נזק, ו/או אובדן, שיבוש או פגיעה במידע כלשהו שנגרם מסיבות של תקיפה חיצונית ו/או זדונית על הארגון.

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Elardus Engelbrecht
2018-06-06 12:34:37 UTC
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Post by Gadi Ben-Avi
I have the following problem.
I need to transfer a very large file (3.7 GB) from a ftp server to z/OS.
First, I tried transferring the file using the z/OS ftp client. It took forever, and then timed out. The average transfer rate was somewhere between 500 and 100 KB/sec.
The transfer kept abending.
What messages are you getting during those abends?
Post by Gadi Ben-Avi
I transferred the file to my pc. That took about 10 minutes. The transfer rate was about 5 MB/sec.
I next transferred the file to z/OS using the windows ftp client and the z/OS ftp server. It took 71 seconds.
Where should I look to find the problem?
I would first turn DEBUG to ALL and then repeat the slow transfer while looking in the FTP.DATA first, but also in the SYSLOG, TCP/IP Stack STC messages, etc.

Look in your FTP.DATA of your z/OS FTP Client to see if some setting is wrong or different from your other FTP.DATA for example VCOUNT, BUFNO, DATACTTIME, DATAKEEPALIVE, DCONNTIME, checkpoint settings.

Groete / Greetings
Elardus Engelbrecht

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Rob Schramm
2018-06-06 13:02:46 UTC
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I am going to guess firewall which is usually my first stop for interrupted
communication. Codes point to a data connection error.

Slowness is not as clear.
- buffers
- data set not allocated properly causing huge number of extents
- wlm
- only as fast as your slowest network segment
- server constraint ( vm cpu, io )

Rob Schramm



On Wed, Jun 6, 2018, 8:34 AM Elardus Engelbrecht <
Post by Gadi Ben-Avi
Post by Gadi Ben-Avi
I have the following problem.
I need to transfer a very large file (3.7 GB) from a ftp server to z/OS.
First, I tried transferring the file using the z/OS ftp client. It took
forever, and then timed out. The average transfer rate was somewhere
between 500 and 100 KB/sec.
Post by Gadi Ben-Avi
The transfer kept abending.
What messages are you getting during those abends?
Post by Gadi Ben-Avi
I transferred the file to my pc. That took about 10 minutes. The transfer
rate was about 5 MB/sec.
Post by Gadi Ben-Avi
I next transferred the file to z/OS using the windows ftp client and the
z/OS ftp server. It took 71 seconds.
Post by Gadi Ben-Avi
Where should I look to find the problem?
I would first turn DEBUG to ALL and then repeat the slow transfer while
looking in the FTP.DATA first, but also in the SYSLOG, TCP/IP Stack STC
messages, etc.
Look in your FTP.DATA of your z/OS FTP Client to see if some setting is
wrong or different from your other FTP.DATA for example VCOUNT, BUFNO,
DATACTTIME, DATAKEEPALIVE, DCONNTIME, checkpoint settings.
Groete / Greetings
Elardus Engelbrecht
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John Eells
2018-06-06 12:56:16 UTC
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How are you using the FTP client? Batch? TSO/E?
Post by Gadi Ben-Avi
Hi,
I have the following problem.
I need to transfer a very large file (3.7 GB) from a ftp server to z/OS.
First, I tried transferring the file using the z/OS ftp client. It took forever, and then timed out. The average transfer rate was somewhere between 500 and 100 KB/sec.
The transfer kept abending.
I transferred the file to my pc. That took about 10 minutes. The transfer rate was about 5 MB/sec.
I next transferred the file to z/OS using the windows ftp client and the z/OS ftp server. It took 71 seconds.
Where should I look to find the problem?
We are running z/OS v2.2
<snip>
--
John Eells
IBM Poughkeepsie
***@us.ibm.com

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Andrew Rowley
2018-06-07 00:10:17 UTC
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Post by Gadi Ben-Avi
I need to transfer a very large file (3.7 GB) from a ftp server to z/OS.
First, I tried transferring the file using the z/OS ftp client. It took forever, and then timed out. The average transfer rate was somewhere between 500 and 100 KB/sec.
The transfer kept abending.
I transferred the file to my pc. That took about 10 minutes. The transfer rate was about 5 MB/sec.
I next transferred the file to z/OS using the windows ftp client and the z/OS ftp server. It took 71 seconds.
I have seen similar issues, but on transfers from z/OS. I was pointed to
APAR PI72242 however I was also on 2.2 and that APAR doesn't apply.
However I suspect that either the fix didn't completely fix the problem,
or it didn't make it into 2.2 TCPIP.

My problem seems to be related to fast networks with a long round trip
time, AKA Long Fat Networks (LFN). To maximize speed TCPIP keeps
increasing the amount of data in transit between ACKs. At some point
z/OS seems to run into trouble with this and you end up with huge
numbers of retransmits and duplicate ACKs. The symptom was transfer
rates slowly increasing, then suddenly plummeting to about 10% of the
peak rate or even less.

If z/OS is sending the data it can't be exactly the same problem, but it
does sound very similar. I found Wireshark very useful to look at the
traffic. Is it possible to run that on the FTP server, or set up a test
system in the same location? That clearly showed when things went bad.

I found that disabling receive window auto tuning on Linux (the
receiving end) with "sysctl net.ipv4.tcp_moderate_rcvbuf=0" prevented
the transfer rate from increasing to the point where it tripped over
into the very slow mode.

There might be a similar parameter on z/OS - if so it would be
interesting to test with z/OS as the receiver.
--
Andrew Rowley
Black Hill Software
+61 413 302 386

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