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Latency and disk utilization increases such as ONTAP shutdown

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ontap-9
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Applies to

Any FAS model with Flash Cache (PAM or NVMe SSD)

Issue

ONTAP may report higher latency following a reboot, shutdown, or upgrade. EMS logs "extCache.warming" or "extCache.aggregate.invalidate" are logged, such as:
Sun Jul 26 09:41:38 -0500 [clus1-02: cf_giveback: extCache.aggregate.invalidate:info]: WAFL external cache: Started deferred invalidations for 2 aggregates.
Sun Jul 26 09:41:38 -0500 [clus1-02: ec_exempt_worker_thread: extCache.aggregate.invalidate:info]: WAFL external cache: Starting deferred invalidation for aggregate in map slot 4.
Sun Jul 26 09:41:38 -0500 [clus1-02: ec_exempt_worker_thread: extCache.aggregate.invalidate:info]: WAFL external cache: Starting deferred invalidation for aggregate in map slot 3.
Sun Jul 26 09:41:41 -0500 [clus1-02: ec_exempt_worker_thread: extCache.aggregate.invalidate:info]: WAFL external cache: Completed invalidation for aggregate in map slot 4 in 3 seconds.
Sun Jul 26 09:41:41 -0500 [clus1-02: ec_exempt_worker_thread: extCache.aggregate.invalidate:info]: WAFL external cache: Completed invalidation for aggregate in map slot 3 in 3 seconds.
Sun Jul 26 09:41:41 -0500 [clus1-02: ec_exempt_worker_thread: extCache.aggregate.invalidate:info]: WAFL external cache: All pending deferred aggregate invalidations have completed.  Total elapsed time: 3 seconds.

Also latency may be seen in System Manager or Active IQ Unified Manager. Here are a couple examples from a system that just went an ONTAP upgrade on July 26, and you can see right at midnight July 27 the latency is slightly higher:

捕获.PNG

ActiveIQ shows the latency increasing in the "Aggregate Ops" Cluster Component, or basically increased latency from the hard drives since the percentage of reads from Flash Cache are less.

捕获2.PNG

 

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