Test Disk Speed from the Linux Command Line

Why test the disk

The speed of the disk decides how quickly a database answers, how fast files load and how long backups take. A slow disk can be the reason why a server feels slow. Test when you buy a server, after a change, or when you see slow I/O.

hdparm: read speed

Install it:

sudo apt-get install hdparm

Test the read speed of a disk (replace sdX with your device, for example sda; find it with lsblk):

sudo hdparm -Tt /dev/sdX

-T tests the cache speed and -t tests the real read speed of the disk.

dd: simple read and write tests

Read test

dd if=/dev/sdX of=/dev/null bs=1M count=1000

• if=/dev/sdX is the input (your disk).
• of=/dev/null throws the output away.
• bs=1M is the block size.
• count=1000 is the number of blocks (about 1 GB).

Write test. This writes a 1 GB file and measures the time. It is safe because it writes to a normal file and not to the device:

dd if=/dev/zero of=./testfile bs=1M count=1000 oflag=direct
rm ./testfile

fio: the flexible tester

fio can imitate real workloads (random or sequential, read or write).

Install it:

sudo apt-get install fio

Create a job file, for example test.fio:

[read_test]
rw=read
size=1G
directory=/path/to/test/directory

Run it:

fio test.fio

Change rw=read to write, randread or randwrite for other tests. The output shows bandwidth (MB/s) and IOPS.

ioping: latency

ioping measures how long a disk takes to answer.

sudo apt-get install ioping
sudo ioping -c 10 /path/to/test/directory

It sends 10 requests and shows the average latency.

How to read the results

• MB/s (bandwidth) matters for large files and backups.
• IOPS matters for databases and many small files.
• Latency matters for how quickly requests are answered.

An SSD or NVMe disk gives much better results than a hard disk. Run each test a few times, and when the server is quiet.

Quick recap

• hdparm -Tt and dd give a fast check.
• fio and ioping give a more detailed picture.
• Never write to the raw device.