Buffer Pool start option


>>-+-----------------------------------------+-----------------><
   '-poolname--=--+-(--)-------------------+-'   
                  '-| Buffer pool values |-'


Buffer pool values

|--(--+--------+--,--+---------+--,--+--------+--,--+---+--,---->
      '-baseno-'     '-bufsize-'     '-slowpt-'     '-F-'      

>--+--------+--,--+--------+--,--+-------------+--)-------------|
   '-xpanno-'     '-xpanpt-'     |         (1) |      
                                 '-xpanlim-----'

Notes:

The IOBUF pool (IO00, IO) is the only buffer pool where all seven values can be specified. For all other buffer pools, the xpanlim field is not supported. If you specify the xpanlim field for any buffer pool other than the IOBUF pool (IO00, IO), even if the field is null, you get an IST1072I message.

Allows you to modify the default buffer pool attributes for the various pools (both basic allocation and dynamic allocation values). Buffer pools are used by VTAM® for holding data or building control blocks. See Buffer pool default values for information about the IBM®-supplied buffer pool values.

For more information on buffer pools, types of buffer pools, and guidelines for basic buffer allocation and dynamic buffer allocation, see z/OS Communications Server: SNA Network Implementation Guide.

poolname

The name of the fixed-length buffer pool to which these options apply.

poolname can be the full buffer pool name, the buffer pool ID, or the abbreviation (for example, either SFBUF, SF00, or SF, respectively, for specifying a small buffer pool in fixed storage).

See Table 1 for a list of the buffer pool names and a description of each buffer pool's function. A complete description of each buffer pool is located in the z/OS Communications Server: SNA Network Implementation Guide.

Table 1. VTAM buffer pools
Poolname	Pool ID	Abbreviation	Use
APBUF	AP00	AP	Used for device related CIBs
BSBUF	BS00	BS	Provides storage for the boundary type 2.1, type 2, and type 1 peripheral node session control blocks
CRA4BUF	CRA4	CRA4	Used for error recovery
CRA8BUF	CRA8	CRA8	Used for error recovery
CRPLBUF	CRPL	CR	Contains the RPL-copy pool
IOBUF	IO00	IO	Used for input/output data
LFBUF	LF00	LF	Provides buffers needed for each active application program and TSO user logged on
LPBUF	LP00	LP	Used for error recovery
SFBUF	SF00	SF	Contains application program information and LU control blocks
SPBUF	SP00	SP	Used for large message (LMPEO) requests
TIBUF	TI00	TI	Contains control information to support HPDT services for HPR or IP
T1BUF	T100	T1	Similar to the TIBUF but larger. Used as a packing buffer by HiperSockets™ accelerator and QDIO. Also used to contain the HPR headers and the media, IP, and UDP headers for an Enterprise Extender connection.
T2BUF	T200	T2	Similar to the T1BUF but even larger. T2BUFs are used exclusively for HiperSockets accelerator and QDIO when the T1BUF is perceived to be of insufficient size to pack all the headers and data. Also used by HPR for all retransmissions over HiperSockets and QDIO.
XDBUF	XD00	XD	Provides storage for the I/O buffer during XID contact processing to peripheral nodes

baseno

range:

1 - 32767

dependencies:

bufsize

Specifies the base number of buffers in the pool. Do not code commas in the value specified.

Note:

The value for baseno should contain the maximum number of buffers that will fit on each page. If baseno is smaller than the maximum number of buffers per page, VTAM adjusts the value to the maximum value.
Storage for buffer pools is allocated by page. After you know the number of buffers per page (for the given bufsize), you can determine the maximum baseno for your environment.
Because storage is allocated by page increments, the amount of buffer storage reserved per page might be less than the size of a page. This storage difference must be considered when determining the value for xpanlim.

bufsize

range:

256-3992 bytes

dependencies:

baseno, IOBUF pool only

Specifies the number of bytes assigned to each buffer in the pool. If you specify a value less than 256, it is changed to 256. If an odd value is specified, it is rounded down to the closest even number.

Note:

The bufsize value specified must allow individual buffers to begin on a doubleword boundary and not expand over a page boundary. See Specifying IOBUF buffer values for specifying IO buffer pool bufsize values.
The value for bufsize does not include header information added to each buffer by VTAM. See Specifying IOBUF buffer values for determining the actual size of each buffer.
The only buffer pool for which you can change the bufsize is IOBUF. You may code the default values for the other buffer pools. If you specify a value other than the default value, a message will be issued and initialization will continue with VTAM using the default values.
Some local SNA controllers, such as 3174, require an even number and will not operate if bufsize is an odd value. To accommodate this requirement, a specification of an odd bufsize value will be rounded down (-1) to the next even value. Refer to the appropriate device description manual for other resource types.

slowpt

dependencies:

baseno

Provides a set of buffers reserved for priority requests (for example, read from a channel-attached device). When the number of available buffers in this buffer pool is equal to or less than this number, buffers are allocated only for priority requests, and normal requests are queued or rejected. This is called slowdown mode.

F

Specifies that the storage for this buffer pool is to be page-fixed. F has meaning only for buffer pools that are normally in pageable storage, but it can be coded for buffer pools that are located in fixed storage by default.

Note:

To use the xpanno and xpanpt operands, but not the F operand, code either double commas or 0 between the slowpt operand and the xpanno operand. For example, coding either:
```
 
LPBUF=(baseno,bufsize,slowpt,,xpanno,xpanpt) 
 or 
LPBUF=(baseno,bufsize,slowpt,0,xpanno,xpanpt) 
```
Causes the buffer pool's default attribute to be used.
See z/OS Communications Server: SNA Network Implementation Guide to determine which buffer pools can be pageable.

xpanno

dependencies:

bufsize

range:

0-32767

Specifies the number of buffers that VTAM acquires when expanding the buffer pool. This value is rounded to the number of buffers that fills the nearest whole page of storage, however the 32767 maximum values cannot be exceeded. For such a case, xpanno is rounded down to the largest number less than or equal to 32767 that will completely fill a whole number of pages.

Note:

If you code 0, dynamic buffering is not performed and the buffer pool never expands. If you do not code xpanno, the IBM-supplied defaults are used.
The use of an xpanno value that is too small for a pool affects run time performance rather than storage utilization. This is because VTAM will be frequently expanding and/or contracting the pool. See z/OS Communications Server: SNA Network Implementation Guide for dynamic expansion guidelines.

xpanpt

range:

(slowpt + 1)-[(baseno - minval) - 1]

Specifies the number of buffers that set the expansion point for this buffer pool. When the number of available buffers in the buffer pool falls to a value that is equal to or less than xpanpt, VTAM expands the buffer pool by the number of buffers defined by xpanno.

Note:

Specify a value for xpanpt so that the buffer pool is not expanded during VTAM initialization.
The value of xpanpt must be greater than the value of slowpt, but less than the difference between baseno and minval. minval is the minimum number of buffers required to open the VTAM ACB and start VTAM. The minval values are listed with the IBM-supplied defaults (see Buffer pool default values).

See z/OS Communications Server: SNA Network Implementation Guide for information and examples of dynamic buffer allocation.

xpanlim

dependencies:

IOBUF pool only, xpanno

range:

0-2097152 Kb

Specifies the total size, in Kb, for this buffer pool including the base allocation and expansions.

VTAM transforms the value of xpanlim into the number of buffers represented by that limit.

Note:

If you code 0, or if you do not specify an xpanlim, buffer expansion is not limited, provided the value for xpanno is nonzero.
If xpanlim is less than the number of bytes in the basic buffer pool allocation, no expansion is performed.
The xpanlim value can be modified after VTAM startup by using the MODIFY BFRUSE command. See z/OS Communications Server: SNA Operation for information about this command.

When a successful expansion of the IO buffer pool brings the total size of the pool to 80 percent (or more) of the expansion limit specified, VTAM scans the IO buffer pool for sessions that are using more than 10 percent of the current size of the buffer pool. Any session using more than 10 percent of the pool receives an IST930I message. This message contains the session partner names as well as the percentage of the pool being used by the session. This happens for each expansion in which the size of the pool is 80 percent or greater of the specified expansion limit.

After VTAM has determined that a session is using more than 10 percent of the IO buffer pool, it checks whether the percentage is greater than or equal to the value specified for HOTIOTRM. If so, VTAM ends the session and any other session between the same resource pair to prevent CSA from being exhausted and possibly causing an outage.