Metrics

Tencent Cloud CBS devices vary in performance and price by type. For more information, see Cloud Disk Types. Because different applications have different workloads, if the number of I/O requests is low, the cloud disk may not play its full performance.
The following metrics are generally used to measure the performance of a cloud disk:

• IOPS: read/write count per second. IOPS varies by the underlying drive type of the storage device.
• Throughput: read/written data volume per second, unit in MB/s.
• Latency: time elapsed from sending an I/O operation to receiving an acknowledgement (in seconds).

Testing Tool

FIO is a tool for testing disk performance. It is used to perform stress test and verification on hardware. This document uses FIO as an example.
We recommend that you use FIO together with libaio’s I/O engine to perform the test. Please install FIO and libaio with reference to Tool Installation.

• To avoid damaging important files in the system, do not perform FIO test on the system disk.
• *To avoid data corruption caused by corruption of the metadata of the underlying file system, do not perform the test on the business data disk. *
• Ensure the /etc/fstab file DOES NOT contain the mount configuration of the disk to be tested. Otherwise, CVM may fail to launch.

Recommended Test Objects

• We recommend that you perform FIO test on empty disks that do not store important data, and re-create the file system after completing the test.
• When testing disk performance, we recommend that you directly test raw data disks (such as /dev/vdb).
• When testing file system performance, we recommend you specify the specific file test (such as /data/file).
  

  Tool Installation

1. Log in to the CVM as instructed in Log in to Linux Instance Using Standard Login Method. Here, take the CVM running CentOS 7.6 OS as an example.
2. Run the following command to check whether the cloud disk is 4KiB-aligned.

   fdisk -lu

   As shown below, if the Start value in the command output is divisible by 8, then the disk is 4KiB-aligned. Otherwise, complete 4KiB alignment before testing.
   
3. Run the following commands in sequence to install the testing tools, FIO and libaio.

   yum install libaio -y

   yum install libaio-devel -y

   yum install fio -y

   Once completed, start testing the cloud disk performance as instructed in the test example below.

Test Example

The testing formulas for different scenarios are basically the same, except the rw, iodepth, and bs (block size) parameters. For example, the optimal iodepth for each workload is different as it depends on the sensitivity of your application to the IOPS and latency.

Parameter description:

Common use cases are as follows:

• bs=4k iodepth=1: random read/write test, which can reflect the latency performance of a disk.
  Run the following command to test the random read latency of the disk:

  fio -bs=4k -ioengine=libaio -iodepth=1 -direct=1 -rw=randread -time_based -runtime=600  -refill_buffers -norandommap -randrepeat=0 -group_reporting -name=fio-randread-lat --size=10G -filename=/dev/vdb

  Run the following command to test the random write latency of the disk:

  fio -bs=4k -ioengine=libaio -iodepth=1 -direct=1 -rw=randwrite -time_based -runtime=600  -refill_buffers -norandommap -randrepeat=0 -group_reporting -name=fio-randwrite-lat --size=10G -filename=/dev/vdb

  Run the following command to test the random hybrid read and write latency performance of an SSD cloud disk:

  fio --bs=4k --ioengine=libaio --iodepth=1 --direct=1 --rw=randrw --time_based --runtime=100 --refill_buffers --norandommap --randrepeat=0 --group_reporting --name=fio-read --size=1G --filename=/dev/vdb 

  The following figure shows the command output:
  

• bs=128k iodepth = 32: sequential read/write test, can reflect the throughput performance of the disk.
  Run the following command to test the sequential read throughput bandwidth:

  fio -bs=128k -ioengine=libaio -iodepth=32 -direct=1 -rw=read -time_based -runtime=600  -refill_buffers -norandommap -randrepeat=0 -group_reporting -name=fio-read-throughput --size=10G -filename=/dev/vdb

  Run the following command to test the sequential write throughput bandwidth:

  fio -bs=128k -ioengine=libaio -iodepth=32 -direct=1 -rw=write -time_based -runtime=600  -refill_buffers -norandommap -randrepeat=0 -group_reporting -name=fio-write-throughput --size=10G -filename=/dev/vdb

  Run the following command to test the sequential read throughput performance of an SSD cloud disk:

  fio --bs=128k --ioengine=libaio --iodepth=32 --direct=1 --rw=read --time_based --runtime=100 --refill_buffers --norandommap --randrepeat=0 --group_reporting --name=fio-rw --size=1G --filename=/dev/vdb

  The following figure shows the command output:
  

• bs=4k iodepth=32: random read/write test, can reflect the IOPS performance of the hard disk.
  Run the following command to test the random read IOPS of the disk:

  fio -bs=4k -ioengine=libaio -iodepth=32 -direct=1 -rw=randread -time_based -runtime=600  -refill_buffers -norandommap -randrepeat=0 -group_reporting -name=fio-randread-iops --size=10G -filename=/dev/vdb

  Run the following command to test the random write IOPS of the disk:

  fio -bs=4k -ioengine=libaio -iodepth=32 -direct=1 -rw=randwrite -time_based -runtime=600  -refill_buffers -norandommap -randrepeat=0 -group_reporting -name=fio-randwrite-iops --size=10G -filename=/dev/vdb

  Test the random read IOPS performance of the SSD cloud disk. This is shown in the following figure: