Buffer pool default values

Table 1 shows the IBM®-supplied values for the buffer pools.
Note:
  1. The bufsize value specified is not the actual length of a buffer; VTAM® adds additional storage to each buffer for buffer management. The amount of storage added is the same for all buffers except for the IOBUF buffer pool.
    • To estimate storage needs for all buffer pools except IOBUF:
      1. Add 16 bytes to the buffer size.
      2. Round bufsize up to a doubleword (multiple of 8).
    • For IOBUF (no encryption specified):
      1. Add 91 bytes to the bufsize value.
      2. Round bufsize up to a doubleword (multiple of 8).
    • For IOBUF, if YES, 24, or 31 is specified on the ENCRYPTN start option:
      1. Add 98 bytes to the bufsize value.
      2. Round bufsize up to a doubleword (multiple of 8).
  2. minval is the minimum number of buffers required to open the VTAM ACB and start VTAM. The minval value is a constant. You cannot change this value.
  3. The minimum value for IOBUF bufsize that will be used by VTAM is 256. If a value less than 256 is specified, then it will be over-ridden to 256 during VTAM initialization. 
    D NET,BFRUSE,BUFFER=IO
IST920I IO00  BUFFSIZE 331
    or 
    D NET,BFRUSE,BUFFER=IO
IST920I IO00  BUFFSIZE 338
  4. The default baseno values for the T1BUF and T2BUF pools are low because these buffers are large. The T1BUF and T2BUF buffers are used only with Enterprise Extender connections that use OSA QDIO or HiperSockets™ as the underlying data link control (DLC). If these buffers are not used in these cases, the buffer pool allocations waste storage if they are defined to be too large. If EE is being used, you typically set the pool allocations for the T1BUF and T2BUF buffers to be greater than their default values. Use IBM Health Checker for z/OS® to check whether the T1BUF or T2BUF baseno values are greater than the default values when Enterprise Extender is not being used. You can also use IBM Health Checker for z/OS to check whether the baseno values are at their default values when Enterprise Extender is being used. For more details about IBM Health Checker for z/OS, see z/OS Communications Server: IP Diagnosis Guide.
Table 1. IBM-supplied VTAM buffer pool values
Buffer pool name baseno bufsize slowpt xpanno xpanpt xpanlim minval
APBUF 56 56 2 1 3    
BSBUF 28 260 0 1 14    
CRA4BUF 50 4080 0 10 20    
CRA8BUF 12 8176 0 6 2    
CRPLBUF 75 144 0 60 29    
IOBUF

55

**1

 256 5 1 6 0  
LFBUF 30 120 0 1 1    
LPBUF 12 2032 0 6 2   4
SFBUF 64 112 0 1 1   5
SPBUF 21 176 0 1 1    
TIBUF 360 Start of change800End of change 0 60 120    
Start of changeT1BUFEnd of change Start of change18End of change Start of change1340End of change Start of change0End of change Start of change36End of change Start of change15End of change Start of change End of change Start of change End of change
T2BUF 8 2028 0 32 7    
XDBUF 5 697 0 1 4    
**This value can change. The IO buffer can be different sizes. VTAM obtains the base number of buffers that actually fit on a 4K page.
Parent topic: Buffer Pool start option