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High host queue depth may trigger node warmstarts on 8.2.1.0 - 8.2.1.5 or 8.3.0.0 software

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Abstract

APAR HU01998 prevents proper handling of excessive host I/O requests, on systems running 8.2.1.0 - 8.2.1.5 or 8.3.0.0. This can occasionally cause node warmstarts during maintenance actions.

Before performing maintenance (including software upgrade) at these software levels, check that host queue depth is correctly configured.

Content

Products based on Spectrum Virtualize software have a fixed number of control blocks available for host I/O requests.
The Knowledge Center configuration guidelines for hosts ensure that hosts do not issue an excessive number of I/O requests. If more I/O requests are received than there are control blocks available, the system reports a SCSI QUEUE FULL response to the host, meaning the host must re-submit the I/O request.
APAR HU01998 prevents proper handling of this condition, and instead of reporting the QUEUE FULL condition, a node warmstart may be seen. If this occurs during an upgrade, when the partner node is upgrading, it may result in an interruption of I/O processing.
Mitigation
When upgrading from software between 8.2.1.0 and 8.2.1.5, or 8.3.0.0, there is a small risk of experiencing this issue. To mitigate the risk, either:
 
  • Confirm that host queue depth settings are configured as recommended in the Spectrum Virtualize documentation, or
  • Schedule a maintenance window to reduce the impact of node warmstarts
Take particular care with VMware hosts, where the default HBA queue depth is normally 256. The recommended setting in the Spectrum Virtualize Knowledge Center is 32. 
References:
Fix
The fix for APAR HU01998 is in 8.2.1.6 and later, and 8.3.0.1 and later.

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Document Information

Modified date:
28 March 2023

UID

ibm16216126

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