How to determine if the LSERV BUFFERPOOL is working with desired performance?

Products

• Common Services
• COMMON SERVICES FOR Z/OS

Issue/Introduction

This document will explain how to determine if the BUFFERPOOLs defined to LSERV are working with desired performance.

Resolution

To check if the BUFFERPOOLs are working with desired performance, enter the following command after some LSERV usage:

/F lservstc, DISPLAY BUFFERPOOL

This command will display all the BUFFERPOOL USAGE and looks something like this:

LDM0552I - File server buffer pools - 
LDM0553I    Pool    Size   Count   BFRFND   BUFRDS    UIW     NUIW 
LDM0554I       1   2,048      80        0        4      0        0
LDM0554I       1   8,192      80        0        2      0        0
LDM0554I       2   2,560      80        0       58      0        0
LDM0554I       2   8,192      40        0      394      0        0
LDM0554I       3   2,048      80   65,406    1,208      0        0
LDM0554I       3   8,192      80    1,507   59,894      0        0
LDM0554I       4   2,048      80        0        0      0        0
LDM0554I       4   8,192      80        0        0      0        0 

This shows 4 buffer pool pairs.
The size column indicates the buffer size in bytes.
The count column indicates the number of buffers that LServ has allocated in that size.

The BUFRND and BUFRDS are the fields which help to evaluate the performance purposes.
In the output, a high number of BFRFND (buffer find) counts relative to BUFRDS (buffer read) counts are desirable for each buffer size.
BUFRND contains the times the data was found in the BUFFERs, and the BUFRDS contains the number of times the BUFFER had to have the data read into it.

For optimal performance, the data LSERV uses should be found in the BUFFERS and not have to be read into them.

Each time DATA is requested by LSERV, it searches first in the BUFFERPOOL for that data. If it is found, the acquire time is rapid. If it is not found, then LSERV has to read the data (I/O) and put the data into the Buffer. This take more time.

The suggested rule of thumb is to try to keep the BUFRDS 10% of the BURFND values and try to make sure that the DATA is in the BUFFERs that will be used most often.

Refer to the LSERV section of the Common Services for z/OS Administrator Guide, for more details about adjusting the size of the Data Buffers and some limitations that can occur.