Azure VM Disk Queue Depth

Disk Queue Depth is the number of outstanding IO requests that are waiting to be performed on a disk. Blue Matador monitors the Data Disk Queue Depth and OS Disk Queue Depth metrics to monitor the queue depth of your Data and OS managed disks for Azure Virtual Machines.

Effects

For some workloads, a high disk queue depth can be acceptable, but for others it should remain very low at all times. IO requests become queued when reads or writes are requested faster than they can be processed by the disk. When IO requests are queued, the total amount of time it takes to read or write data to disk will be greater.

Fixes

The appropriate fix depends heavily on your application, the number of IO operations being performed, and the size of those operations. If disk queue depth is leading to degraded performance in your application, the following solutions can help alleviate IO on the affect disk(s):

• Reduce the number or size of reads and writes being performed
• Upgrade the disk to a higher tier or increase disk size to get better IO performance and/or more IOPS
• Split IO activity across multiple disks

Resources

• Azure premium storage: design for high performance (Microsoft Azure Documentation)
• Scalability and performance targets for VM disks on Windows (Microsoft Azure Documentation)