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Heavy SMB signing pressure causes high SMB3 latency from Network CPU domain

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Category:
ontap-9
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perf
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Applies to

  • Versions of ONTAP prior to 9.7
  • SMB3
  • SMB2

Issue

  • High SMB latency from Unified Manager, Grafana.
    • In the latency breakdown section, the bulk of the latency is from Network or CPU N-blade, depending on the tools that are used to monitor performance
  • The impacted Vservers have a large amount of SMB3 or SMB3.1 connections
cluster1::> set -c off advanced
cluster1::*> statistics start -node node1 -object cifs -counter total_smb3_1_connections_count|total_smb3_connections_count
cluster1::*> statistics show -sample-id sample_1

Object: cifs
Instance: testsvm
Start-time: 11/22/2021 15:39:20
End-time: 11/22/2021 15:42:00
Elapsed-time: 160s
Scope: testsvm

    Counter                                                     Value
    -------------------------------- --------------------------------
    total_smb3_1_connections_count                               1031
    total_smb3_connections_count                                 1254
  • The impacted Vservers have signed sessions, as well as a significant amount of data being signed per second
cluster1::*> statistics start -node node1 -object smb2 -counter bytes_signed_rate|signed_sessions
cluster1::*> statistics show -sample-id sample_2

Object: smb2
Instance: testsvm
Start-time: 11/22/2021 15:48:17
End-time: 11/22/2021 15:49:05
Elapsed-time: 48s
Scope: testsvm

    Counter                                                     Value
    -------------------------------- --------------------------------
    bytes_signed_rate                                       10240000B
    signed_sessions                                               128
  • Network CPU is not necessarily saturated
    • Avg CPU might NOT be high
    • Nwk_Exmpt CPU domain from systat -M
  • Other protocols might be impacted as well, such as NFS or iSCSI. As they have to complete for the same network threads with SMB signing workload

 

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