Storage QoS

Storage QoS allows you to limit the I/O throughput and IOPS for VMs that do not run key services to ensure high performance of VMs that offer key services.

Limit the I/O throughput and IOPS

About the I/O throughput and IOPS

The relationship between the I/O rate and IOPS is as follows:

I/O rate in MiBps = IOPS × data block size / 1024

As shown in Figure-1, the I/O throughput rises and the IOPS drops as the data block size increases. When a disk transmits large data blocks, it takes the disk more time to perform an I/O operation, and the IOPS drops accordingly. Because a large data block contains more data than a smaller one, the I/O throughput increases with the data block size. If you limit both the I/O throughput and IOPS, the first reached limit takes effect.

Figure-1 Impacts of data block size increase on I/O throughput and IOPS

 

·          After you set the IOPS or I/O rate limits for a VM, you do not need to reboot the VM. ·          To ensure correct VM startup and operation, set the I/O rate limits to be larger than 8000 KBps, and set the IOPS limits to be smaller than 300.

Procedure

1. On the top navigation bar, click Resources.

2. From the left navigation pane, select Host Pool Name > Cluster Name > Host Name > VM Name or Host Pool Name > Host Name > VM Name.

3. Click Edit.

4. Expand advanced settings on the Disk tab.

5. Configure the following parameters:

• I/O Limit: Enter the I/O read and write rate limits in KBps.

• IOPS Limit: Enter the IOPS read and write limits.

Figure-2 Editing advanced disk settings

 

Set the I/O priority

About I/O priorities

An I/O priority determines the sequence in which VMs access the physical disks of a host when the VMs are competing for storage resources. When storage resources are insufficient, the VMs with high I/O priority take precedence.

I/O priorities can be high, medium, or low. The system allocates disk resources to VMs with high, medium, and low I/O priorities in a ratio of 5:3:2.

Procedure

1. On the top navigation bar, click Resources.

2. From the left navigation pane, select Host Pool Name > Cluster Name > Host Name > VM Name or Host Pool Name > Host Name > VM Name.

3. Click Edit.

4. Expand advanced settings on the Summary tab.

5. Set the I/O priority.

Figure-3 Setting the I/O priority