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CONTAP-825756: pNFS clients may stop receiving layouts after upgrade to ONTAP 9.18.1, causing all NFS I/O to be served through a single LIF

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ontap-9
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nas
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Issue

After upgrading to ONTAP 9.18.1, some pNFS device entries may be left in a state where the device is reported as available but has no associated device mappings. NFSv4.1 clients that request a layout for files on an affected volume receive NFS4ERR_LAYOUTUNAVAILABLE and send all I/O for that volume through the LIF used to mount the export, instead of directly to the node that owns the data.
Symptoms include:
  • Increased NFS latency, especially for small-file workloads, after the upgrade.
  • I/O concentrated on the mount LIF and its node instead of being spread across the cluster.
  • In severe cases, slow or failing client mounts.

The condition does not clear on its own.
An affected device can be identified at advanced privilege level. The device is listed with a Mapping Status of "available":
vserver nfs pnfs devices show -vserver <svm> -mapping-status available
but no rows are returned for its Mapping ID:
vserver nfs pnfs devices mappings show -vserver <svm> -global-device-table-id <mapping-id>

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