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访问主机上的LUN时、等待并获取高

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适用场景

  • ONTAP 9
  • FCP
  • iSCSI

问题描述

  • 访问ONTAP 上托管的LUN时、主机上出现速度缓慢的情况。
  • 从主机观察到等待时间较长且利用率较高。

示例:high await%util 并从RedHat Linux中观察到

iostat.jpg

注:

  • 其他主机将采用不同的方法来衡量等待时间和利用率。
  • 对于RedHat Linux、请参见"故障排除"了解iostat -x输出以了解其含义 await%util
  • 中可能会报告高延迟、也可能不会报告高延迟 qos statistics volume latency show。 
    • 如果SAN Opsize很小、大多数小于64 KB、则不会报告高延迟。 
    • Networkqos statistics volume latency show当SAN Opsize较大时、中的列报告了高延迟、大多数情况下大于64 KB。
    • 原因是: 
      • 如果Opsize大于64 KB、则SAN操作将拆分为多个PDU。这些PDU之间的往返时间也会计入ONTAP 报告的延迟、这会将外部因素影响到整体延迟。例如交换机或之间的网络。
      • 如果Opsize小于64 KB、则ONTAP 延迟不会考虑外部因素。 
      • 有关详细信息、请参阅Why is the reported LUN latency Higher than the volume latency?
  • 有一种趋势是Tx/Rx FC光功率值下降、可以使用命令进行验证:

Cluster::> fcp adapter show -node xxxxx -adapter xx

示例:

Received Optical Power   570.7 (uWatts)
SPF Transmitted Optical Power   123.8 (uWatts)

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