Improving System Performance During Heavy FTP Usage

Question

How can I reduce the system overhead associated with multiple concurrent FTP sessions?

Cause

A separate copy of the FTP executable code must be kept for each address space associated with an active FTP connection (both client and server). This leads to increased demands on system storage resources as the number of concurrent users rises, especially if there are peak periods of scheduled file transfer activity. The conventional solution of placing the library containing these modules in the LPALST will not work, since these are program objects instead of conventional load modules.

Answer

Use the Dynamic LPA feature of z/OS to load a copy of the modules into common storage.

Advantages:

• Reduced demand on system storage resources during periods having higher volumes of FTP connections. This includes:
  • Auxiliary (AUX) storage
  • Paging rates
  • Real storage
• Reduction in CPU usage and FTP response delays, since the associated program code does not have to be copied into new address spaces.
• Page frames for code associated with low use features (such as JES spool access or SQL queries using FTP) will tend to stay paged out.
• Under certain system configurations, this can also reduce I/O to the DASD volume containing the SEZALOAD data set.

• You will need 1.8M of ECSA for the two server modules, plus another 1.5M for the client (figures based on z/OS 1.9 module sizes). You may have to increase the size of ECSA specified on the CSA statement in the IEASYSxx PARMLIB member to accommodate the increased demand.
• If any maintenance is applied (without an IPL), remember to also load the new copy into ECSA (and remove the old after the user address spaces terminate).
• This method is not recommended for z/OS 1.4 or earlier releases. The FTP modules reside in below-the-line storage in those releases.
• Benefits will not be significant on systems with low volumes of FTP usage.

Use the following SETPROG LPA,ADD commands to add the FTP modules to Dynamic LPA. You can add these to the COMMNDxx PARMLIB member so that it is performed automatically at IPL.

FTP Server: SETPROG LPA,ADD,MODNAME=(EZAFTPLD,FTPD),DSNAME=LNKLST SETPROG LPA,ADD,MODNAME=(EZAFTPLS,FTPDNS),DSNAME=LNKLST

FTP Client:

SETPROG LPA,ADD,MODNAME=(EZAFTPLC,FTP),DSNAME=LNKLST

Notes:

• The DSNAME specification assumes that the SEZALOAD data set is in the Linklist.
• You can also specify the PAGEPROTPAGE keyword to provide a minor reduction in the ECSA storage used. If specified, this can leave a portion of the modules unprotected.