SQA/CSA thresholds

Ensuring the appropriate size of the extended SQA and extended CSA storage is critical to the long-term operation of the system.

If the size allocated for SQA is too large, the thresholds for the IRA100E and IRA101E messages will not be met and CSA can become exhausted and cause a system outage. One way to avoid this problem is to allocate the minimum SQA required or allow for some CSA conversion so that the storage thresholds that trigger the IRA100E and IRA101E messages are based only on the remaining CSA.

If the size allocated for extended SQA is too small or is used up very quickly, the system attempts to use extended CSA. When both extended SQA and extended CSA are used up, the system allocates space from SQA and CSA below 16 megabytes. The allocation of this storage could eventually lead to a system failure.

When the size, in bytes, of combined total of free SQA + CSA pages falls below the "high insufficient" threshold, the system issues message IRA100E
If the size, in bytes, of available SQA and SQA pages falls below the "low insufficient" threshold, the system issues message IRA101E
If storage is freed such that the available SQA+CSA amount reaches the "high sufficient" threshold, the system issues message IRA102I

The following conditions may be responsible for a shortage of SQA/CSA:

There has been storage growth beyond the previous normal range.
Allocation of SQA and/or CSA is inadequate.
The current thresholds at which the IRA100E and/or IRA101E messages are issued are too high for your installation.

Note: IBM® recommends that you do not change the storage thresholds set by the system. Setting the thresholds too low can hamper the ability of the system to recover from storage shortages and may result in unscheduled system outages. Setting the thresholds too high can cause IRA100E, IRA101E, and IRA102I messages to be issued excessively. If you do change the storage thresholds, you should be sure that the threshold is not being reached because of a problem in the system or inadequate allocation of CSA/SQA.

The SQA/CSA threshold levels are contained in the IGVDCLIM CSECT in load module IEAIPL04. Table 1 shows the offsets of the threshold values.

Table 1. Offsets for the SQA/CSA threshold levels
Offset	Default Value	System Enforced Minimum	Description	Comments
0000	x'41000'	x'9000'	Sufficient space high	IRA102I message issued at this threshold
0004	x'21000'	x'5000'	Sufficient space low	IRA102I message issued at this threshold
0008	x'40000'	x'8000'	Insufficent space high	IRA100E message issued at this threshold
000C	x'20000'	x'4000'	Insufficient space low	IRA101E message issued at this threshold

If you change the default thresholds, make sure that the new sufficient threshold values are at least x'1000' larger than the insufficient values. The new values become effective at the next IPL.