V5R1 puts FTP in its own SBSD place

V5R1 provides a new facility that allows you to balance FTP processing requirements against OS/400 system requirements.

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Prior to OS/400 V5R1, one of the work management issues with FTP was that no matter what you did your iSeries or AS/400 always ran the batch jobs that service FTP requests in the QSYSWRK subsystem. The problem with this setup is simple. FTP can eat up a lot of system resources as it converts and exchanges OS/400 files with other computers, slowing down other server jobs in the process. And if you use your machine to provide a file download...

service -- where many users may be downloading large files at the same time -- the competition between FTP and other necessary server jobs can create a bottleneck on limited system resources, such as main memory and activity levels.

With V5R1, the situation has changed. In V5R1's FTP attributes, you can now specify which subsystem you want FTP to run in, configure an FTP-centric subsystem description if it doesn't already exist, and start the FTP subsystem whenever the FTP server is started. The result is that you can easily configure a private FTP subsystem inside OS/400 V5R1 and then move your FTP server jobs to that subsystem simply by changing one new FTP attribute. Here's how it works on both the green-screen and in the iSeries Operations Navigator program that comes with Client Access Express for Windows V5R1M0.

Using it on the green screen
On the green screen, you enable this new capability through the Change FTP Attributes (CHGFTPA) command. CHGFTPA defines several working parameters OS/400 uses to manage FTP access for external users. In V5R1, IBM added a new subsystem description parameter (SBSD) that allows you to specify the description of the subsystem where you want the FTP server jobs to run. The SBSD parameter consists of two entry fields that define the name of the subsystem description and the OS/400 library that description resides in. By default, this parameter lists the QSYSWRK description in library QSYS as FTP's hosting subsystem. To redirect FTP server jobs to another subsystem under V5R1, you simply modify the SBSD parameter to list the name and library where your preferred subsystem's description is stored. Once you input the new subsystem description location, all you have to do to move FTP out of QSYSWRK is to end and restart the OS/400 FTP server by using the End TCP/IP Server (ENDTCPSVR) and Start TCP/IP Server (STRTCPSVR) commands, as follows:

ENDTCPSVR SERVER(*FTP)
STRTCPSVR SERVER(*FTP)

Once the server is restarted, the FTP server jobs will now be running in the subsystem you specified in CHGFTPA. (To locate your FTP server jobs, look for any jobs whose names match the QTFTPnnnnn format, where nnnnn is a five-digit number.) If the subsystem isn't active when you issue the STRTCPSVR command, OS/400 will start the subsystem as it starts FTP. It's pretty simple.

How it works on OpsNav
This change can also be activated inside iSeries Operations Navigator V5R1M0. To change your FTP subsystem in OpsNav, open the Network-Servers-TCP/IP node and right click on the FTP entry. On the pop-up menu that appears, select Properties and you can change the FTP subsystem definition under the General tab on the FTP Properties dialogue. The FTP server can then be stopped and restarted in OpsNav by right-clicking on the FTP entry again and selecting the Stop and the Start options from the pop-up menu.

There are a few things to consider when you change your FTP subsystem. First, make sure that you list the correct library name for your new FTP subsystem name in CHGFTPA. After you enter the preferred description location, OS/400 will check for an already-active subsystem with the same name as the subsystem name you entered. And if the active subsystem's description resides in a different library than the one you entered in your CHGFTPA parameter, CHGFTPA will return an error. So be careful to specify the right description name and library.

Second, if the subsystem description doesn't already exist on your system, CHGFTPA will create a new basic subsystem description in the designated library. OS/400 will also create the job queues that are used to feed jobs into this subsystem. That means you will need the proper OS/400 authorities to the target library and the authority to create a subsystem description and an output queue. Also, since CHGFTPA is using a standard template for creating the new subsystem, that subsystem may use the same *BASE storage pool and activity levels that you were trying to remove the FTP server jobs from when they were running under QSYSWRK. So if you don't assign the FTP subsystem to a different storage pool than what your system is using for its QSYSWRK jobs, you may not see much benefit in assigning FTP to a different subsystem. You need to consider the work management issues of this change, so be sure to use the Work with Subsystem Description (WRKSBSD) command to edit any new subsystem descriptions for the proper storage pool definitions, activity levels, etc. that your system requires.

With this change, IBM provides a new facility that allows you to balance FTP processing requirements against OS/400 system requirements. If your system runs large FTP jobs that consume a lot of system resources, you may want to check out this new feature to see if it can help you improve system performance.

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About the author: Joe Hertvik is an IT professional and freelance writer who has been working with OS/400 since the days of the System/38 in the mid-1980s. Joe can be reached at jhertvik@midrangeserver.com.

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This was first published in December 2001

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