(1) .-QDIOSTG--=--MAX-------. >>-+-----------------------+----------------------------------->< '-QDIOSTG--=--+-MAX-+---' +-AVG-+ +-MIN-+ '-nnn-'
- QDIOSTG defaults to MAX for 64-bit (z/Architecture®) machines and MIN for non 64-bit machines.
Specifies how much storage VTAM® keeps available for read processing for all OSA QDIO data devices. Units are defined in QDIO SBALs (QDIO read buffers). Each SBAL is 64k. For most users the default setting will be the most suitable option. The storage used for this read processing is allocated from CSM data space 4k pool, and is fixed storage.
The IBM® recommended values can be configured by specifying MAX, AVG, or MIN, which are predefined constants (number of SBALs) that are most appropriate for this type of adapter. MAX allows for the best performance (for example, throughput), but requires more storage. Conversely, MIN could be used for devices with lighter workloads or where system storage might be constrained. Also instead of using one of the 3 predefined values, users can instead define a specific value for QDIOSTG (the exact number of SBALs), such as QDIOSTG=100. The supported range is 8 (minimum supported value) to 126 (maximum supported value). The predefined and possible user-defined values for QDIOSTG are the following items:
- QDIOSTG=MAX
- Specifies the recommended maximum (64 SBALs for a total of 4 MB). This is the default for 64-bit z/Architecture machines.
- QDIOSTG=AVG
- Specifies the recommended average (32 SBALs for a total of 2 MB).
- QDIOSTG=MIN
- Specifies the recommended minimum (16 SBALs for a total of 1 MB). This is the default for non 64-bit z/Architecture machines).
- QDIOSTG=nnn
- Specifies the user defined specific number of SBALs, valid range of 8 - 126 (see Guideline 4).
- If you elect to define a specific value, carefully evaluate your system storage and performance needs for your QDIO devices. The following calculation is used to determine the amount of storage used: (NNN x 64K) x number of active inbound queues for each active QDIP data device. When QDIO inbound workload queueing (IWQ) is not enabled, only one inbound queue is active for each active device. When IWQ is enabled, one or more ancillary input queues might also be active. See QDIO inbound workload queueing in z/OS Communications Server: IP Configuration Guide to determine how many ancillary input queues are enabled for each QDIO data device.
- You can use VTAM tuning stats to evaluate your needs and usage. Under a sample (typical) workload, the NOREADS counter should remain low (close to 0). If this count does not remain low you might need to consider a higher setting for QDIOSTG.
- You can override the QDIOSTG value for a given OSA-Express QDIO device by using the READSTORAGE parameter on the IPAQENET LINK, the IPAQENET INTERFACE, or the IPAQENET6 INTERFACE statement in the TCP/IP profile.
- Each active OSA-Express QDIO DATAPATH device consumes a large
amount of fixed storage. Defining a large number (for example, 8 or
more devices per z/OS® image)
of QDIO devices can cause z/OS Communications
Server to consume a significant amount of fixed storage. This could
lead to degradation of overall system performance. When configuring
a large number of devices, it is important to use the controls provided
to manage and tune the amount of fixed storage consumed by these devices.
Review the following parameters with this in mind:
- VTAM QDIOSTG start option
- READSTORAGE specifications in the TCP/IP profile
- FIXED MAX specification in the IVTPRM00 parmlib member for Communication Storage Manager (CSM).