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External cache shows both usage and hit_percent are 0 after node reboot even if -is-rewarm-enabled is set to true

  1. Last updated
    Apr 21, 2025
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14
Visibility:
Public
Votes:
0
Category:
ontap-9
Specialty:
core
Last Updated:
4/21/2025, 9:23:42 AM

Applies to

  • FAS
  • AFF 
  • ONTAP 9
  • Flash Cache

Issue

  1. Before the node reboot, statistics shows there have data block hit and usage in the flash cache :

     ::*> statistics show -sample-id test

     Object: ext_cache_obj
     Instance: instance_name
     Start-time: 3/11/2025 23:49:43
     End-time: 3/12/2025 00:05:54
     Elapsed-time: 971s
     Scope: Node-01

      Counter                                                     Value
      -------------------------------- --------------------------------
      hit_percent                                                   31%
      size                                                          880
      usage                                                          86

  2. The node was reboot at an hour ago with  -is-rewarm-enabled is set to true:
    Wed Mar 12 01:52:02 +0900 [Node-01: ec_warming_control_thread: extCache.rw.start:debug]:
    Wed Mar 12 01:52:27 +0900 [Node-01: ec_warming_control_thread: extCache.rw.complete:debug]:
    Wed Mar 12 01:52:27 +0900 [Node-01: ec_warming_control_thread: extCache.rw.replay.start:info]: WAFL external cache warming replay has begun for aggregate aggr01_0.
    Wed Mar 12 01:52:27 +0900 [Node-01: ec_warming_control_thread: extCache.rw.replay.complete:info]: WAFL external cache warming replay complete for aggregate aggr01_0 with invalidation log 0%% full.
    Wed Mar 12 01:52:37 +0900 [Node-01: svc_queue_thread: extCache.QoS:info]: External Cache QoS is: Enabled.
    Wed Mar 12 01:53:21 +0900 [Node-01: ec_exempt_worker_thread: extCache.aggregate.invalidate:info]: WAFL external cache: Starting invalidation for aggregate in map slot 2.
    Wed Mar 12 01:53:56 +0900 [Node-01: ec_exempt_worker_thread: extCache.aggregate.invalidate:info]: WAFL external cache: Completed invalidation for aggregate in map slot 2 in 35 seconds.
  3. statistics show both usage and hit_percent are 0 during 5 minutes window after then.

::*> statistics show -sample-id test

Object: ext_cache_obj
Instance: instance_name
Start-time: 3/12/2025 02:42:44
End-time: 3/12/2025 02:46:10
Elapsed-time: 206s
Scope: Node-01

  Counter                                                     Value
  -------------------------------- --------------------------------
  hit_percent                                                    0%
  size                                                          880
  usage                                                           0

 

 

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