Reads Exhausted are the number of times within the sampling interval
where there were no read buffers available to the OSA or HiperSockets
device upon entry to the queued direct I/O (QDIO) program-controlled
interrupt (PCI) Exit.
If this value is not zero, this might
indicate a lack of read buffers for the queued direct I/O (QDIO) datapath
device. It is likely a lack of read buffers will result in dropped
packets and therefore packet retransmission. This situation
is caused by the OSA or HiperSockets device overrunning the queued
direct I/O (QDIO) program-controlled interrupt (PCI) Exit. To help
prevent a Reads Exhausted condition, provide the device with a larger
set of SBALs (Storage Block Address Lists). An SBAL is a set of 16
4K read buffers and therefore a 64K read buiffer. A maximum of 126
SBALs are allowed. Issue the Display TRLE VTAM command and note the
value displayed for message IST2333I. Note the number of SBALs under
the READ STORAGE header. If possible, increase this value to help
prevent a Reads Exhausted condition.
For information about how many
SBALs VTAM allocates by default for each OSA-Express QDIO and HiperSockets
interface, how to control the amount of this storage allocation using
the VTAM QDIOSTG start option (for OSA-Express QDIO) and the VTAM
IQDIOSTG start option (for HiperSockets) see the IBM
z/OS Communications Server: SNA Resource Definition Reference.
The READSTORAGE parameter for the DEVICE/LINK and INTERFACE statement
overrides the QDIOSTG and IQDIOSTG parms. For more information, see
the IBM z/OS Communications Server IP Configuration Reference.
If the number of SBALs is already at the maximum,contact IBM Software
Support to determine if there are other reasons for the reads exhausted situation
to occur.
This is a critical situation.
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