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Flash Cache is stuck in rewarming phase and does not accept insertions

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573
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Category:
ontap-9
Specialty:
perf
Last Updated:

Applies to

ONTAP 9.3P8 and earlier releases

Issue

Flash Cache is stuck in rewarming phase and does not accept insertions with the following symptoms:

  • High latency from Disk layer
  • High Disk utilization
  • Low cache insert/hit rate in Flash Cache

To confirm the low cache insert/hit rate in Flash Cache:

Example:

cluster::> set advanced

Warning: These advanced commands are potentially dangerous; use them only when directed to do so by NetApp personnel.
Do you want to continue? {y|n}: y

cluster::*> statistics start -sample-id <test1> -object ext_cache_obj -counter inserts|hit_percent|rewarm_aggrs_failed
Statistics collection is being started for sample-id: test1

fas8200-2n-dal-1::*> statistics stop -sample-id <test1>
Statistics collection is being stopped for sample-id: test1

fas8200-2n-dal-1::*> statistics show -sample-id <test1>

Object: ext_cache_obj
Instance: ec0
Start-time: 5/18/2021 10:43:17
End-time: 5/18/2021 10:43:25
Elapsed-time: 8s
Scope: cluster-1a

    Counter                                                     Value
    -------------------------------- --------------------------------
    hit_percent                                                    0%
    inserts                                                         0

Object: ext_cache_obj
Instance: ec0
Start-time: 5/18/2021 10:43:17
End-time: 5/18/2021 10:43:25
Elapsed-time: 8s
Scope: cluster-1b

    Counter                                                     Value
    -------------------------------- --------------------------------
    hit_percent                                                    0%
    inserts                                                         0
4 entries were displayed.

Notes: 

  • hit_percent should be 0%, indicating no cache hits
  • inserts should be lower than 10/s, indicating no data is being inserted into Flash Cache

 

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