Slow FTP transfer between Mainframe with OSA card and Windows 2008 Server

We are trying to increase the speed of FTP transfters of a 1GB file from our ZOS Mainframe to a Windows 2008 Server.  Currently we transfer a 1GB file, over a 1Gbps link, at speeds close to 28500Kbytes/sec.  This takes close to 40 seconds to complete.  I have tried doing this ftp between the mainframe and a windows 2003 server and played with the TCP windows sizing and nothing I tweak seems to help.  On the 2008 server I've tweaked the autotuning level by disabling it and this doesn't help.  I currently have the mainframe directly connected to the windows server with a cross over cable to eliminate any network slowness.  I get the same kind of speeds when I transfer this file over the network also.  I have directly connected two windows servers and done the ftp with 100492Kbytes/sec for the same 1GB file and it's done in about 10 seconds.  We have also played with the window size on the mainframe at 64K, 128K and 256K and these settings don't seem to make any drastic improvements.  Has anyone else out their worked with transfering files via FTP from a mainframe to a Windows server and got good speed results?
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It sounds like you might be using Jumbo frames on the Windows box and default of 1500 on z/OS.  Jumbo frames is the only way Windows will get that speed.  In fact, what type of SAN system is connected to the Windows.  

The best we have ever got going from z/OS to Windows is about 40Mbytes/sec.  z/OS to z/OS over Gigabit Ethernet and jumbo frames we get 100Mbps.

What level of z/OS are you running and which OSA's do you have?
Oh couple more questions

Which zSystem server are you running on?  What is the CPU utlization when you are doing the transfer?

Is the file a text file?  Transferring in text mode on z/OS can be very CPU intensive doing EBCDIC to ASCII conversion.
lsysamcAuthor Commented:
From what we understand, the only way to get jumbo frames from ZOS is to use the OSA Express 2 card and we only have the OSA Express card.
We are running ZOS 1.8 with OSA Express.  
There is plenty of CPU available durning the FTP.
We are FTPing  all files in BINARY, so there is no conversion.
We currently have this OSA Express card directly attached to the Windows 2008 server with a cross over cable so I don't think the MTU size makes a difference.  And changing the window size on the mainframe doesn't help either.  So I take it you have the OSA Express 2 card?  Did you get this card because of speed issues you were having?  Anything else that you can think of that could help us or is there some web sites we should check out?
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I will need to double check, but so far everything I have found says that you can use jumbo (up to 8992 is the recommendation) on OSA-Express.

When you do the Windows to Windows transfer are you using jumbo frames?

Is the MTU the same on z/OS and Windows (either both 1500 or both 1492).

Even with the computers directly connected MTU matters.  The smaller the MTU the more work the CPU has to do, for a distributed box the more CPU interrupts there are which drasticly reduces through-pyt.  With Jumbo you can get MTU up to 8992 bytes (limit on OSA) which is just about the same as six 1500 byte MTU's.  That just about 5 fewer interrupts on the distributed side for about every 9,000 bytes of data.

I will have to check, I thought we only had Expresses.  If we have Express2 that is because that is what came with the box when we did our last upgrade.

I don't know if your on the z/OS side or not, but if you are you can issue the netstat dev (TSO) or netstat -d (Unix System Services) and look at the ActMtu in the results to see what the physical MTU is.
lsysamcAuthor Commented:
We had some progress today.  Your note got me thinking about the Jumbo Frames so I looked at our test Windows 2008 server and on the nic card I noticed that Jumbo Packed was disabled.  After we enabled this, it improved our file transfers up to almost 40MB/s or it took us 30 seconds instead of 40 seconds to tranfer a 1GB file.  So this makes me think about what you said earlier.  When you say the best you got between windows and ZOS is 40MB, which is what were seeing now, was this with Jumbo on a OSA Express card or Jumbo on a OSA Express 2 card?  Do you have a OSA Express 2 card now and if so what speed do you get going to a Windows server?
Just checked, we do have OSA Express 2.  From my testing and experience when using 1500 byte frames the best you can get is 40MB/sec.

Did you mean "Jumbo Packed" or "Jumbo Packets?"

Right no I have no access to an enviroment where I can test using Jumbo frames.  I do seem to remember getting in the 70-80MB/sec range doing early ftp testing to/from a distributed box, but I was told that was the limitation of the I/O rate on the distributed boxes disk system.

IIRC the biggest difference between the OSA Express and the "2" card is the ability to do TCP packet segmentation offload, but this was broken badly and the last I checked IBM's recommendation was to leave it disabled.  With segmentation enabled, it could disable the OSA adapter and if you don't have a second one, you loose access to your system.   In some instances it was an IPL to get it back.  We had it happen to us, but luckily we had a second OSA for backup and recovered the OSA without an IPL.  There may have been a slight performance improvement between the Expresss and the "2".

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