Hello,
I think this thread and the article inside will help you on your question :
https://social.technet.microsoft.com/Forums/windowsserver/en-US/8243358e-435a-43c4-b2c2-aa07979d3e5a/performance-monitor-and-avg-disk-queue-length?forum=winservergen
Disk queue length :
Tracks the number of requests that are queued and waiting for a disk during the sample interval, as well as requests in service
This counter will help you understand if you have disk performance issue
Disk tuning and performance :
https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-2000-server/cc938959(v=technet.10)?redirectedfrom=MSDN