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Modifying queue depth and timeouts
16 Dell EMC SC Series: Best Practices with VMware vSphere | 2060-M-BP-V
4.5 Adaptive queue depth
At times of high congestion, VMware has an adaptive queue depth algorithm that can be enabled with the
QFullSampleSize and QFullThreshold variables. These variables aid in relieving the congestion by
dynamically reducing and increasing the logical unit number (LUN) queue depth. Due to the architecture of
SC Series storage, enabling these settings is not recommended unless under the guidance of Dell Support.
For more information, see Controlling LUN queue depth throttling in VMware ESX/ESXi in the VMware
Knowledge Base.
4.6 Modifying the guest operating system queue depth
The queue depth can also be set within the guest operating system if needed. Windows operating systems
have a default queue depth of 32 set for each vSCSI controller, but can be increased up to 128 if necessary.
The method to adjust the queue depth varies between operating systems. Examples are shown in section
4.6.1. Extra vSCSI adapters can be added to a virtual machine to increase the total queue depth available to
the virtual machine.
4.6.1 Windows Server
To adjust the queue depth for the LSI
®
Logic drivers, add or modify the following registry keys:
1. Before beginning, back up the registry.
2. Use regedit to add the following keys:
a. For LSI Logic Parallel (LSI_SCSI):
Windows Registry Editor Version 5.00
[HKLM\SYSTEM\CurrentControlSet\Services\LSI_SCSI\Parameters\Device]
"DriverParameter"="MaximumTargetQueueDepth=128;"
; The semicolon is required at the end of the queue depth value
"MaximumTargetQueueDepth"=dword:00000080
; 80 hex is equal to 128 in decimal
Registry settings for the LSI Logic Parallel vSCSI adapter