Storage driver options in Docker - Commands & Configuration

Introduction

Docker uses storage drivers to manage how data is stored and shared between containers and the host system. Choosing the right storage driver helps keep your containers fast and your disk space organized.

When you want to improve container performance by selecting a storage method optimized for your system.

When you need to troubleshoot issues related to container file storage or disk usage.

When setting up Docker on a new server and want to configure storage for best compatibility.

When running multiple containers that share data and you want to control how that data is stored.

When upgrading Docker and want to switch to a newer storage driver for better features.

Commands

This command shows the current storage driver Docker is using on your system.

Terminal

docker info --format '{{.Driver}}'

Expected Output

overlay2

Starts the Docker daemon using the overlay2 storage driver, which is recommended for most modern Linux systems for better performance and stability.

Terminal

dockerd --storage-driver=overlay2

Expected Output

INFO[0000] Starting up

INFO[0000] Using storage driver overlay2

→

--storage-driver - Specifies which storage driver Docker should use

Runs a temporary Alpine Linux container to test that Docker is working with the chosen storage driver.

Terminal

docker run --rm -it alpine sh

Expected Output

/ #

→

--rm - Automatically removes the container after it exits

→

-it - Runs the container interactively with a terminal

Key Concept

If you remember nothing else from this pattern, remember: the storage driver controls how Docker saves and shares container data on your system.

Common Mistakes

Trying to change the storage driver without restarting the Docker daemon.

Docker needs to restart to apply a new storage driver; otherwise, it keeps using the old one.

Stop Docker, change the storage driver setting, then start Docker again.

Using a storage driver not supported by the host operating system.

Unsupported drivers can cause Docker to fail or behave unpredictably.

Check Docker documentation for supported storage drivers on your OS before changing.

Ignoring the current storage driver and trying to troubleshoot storage issues blindly.

Different drivers have different behaviors; knowing the driver helps diagnose problems correctly.

Always check the current storage driver with 'docker info' before troubleshooting.

Summary

Use 'docker info --format '{{.Driver}}'' to check which storage driver Docker is using.

Set the storage driver by starting the Docker daemon with the '--storage-driver' flag.

Test your Docker setup by running a simple container to ensure storage works correctly.

Practice

1. What is the main purpose of a Docker storage driver?

easy

A. To manage how Docker stores container data on disk

B. To control network settings for containers

C. To schedule container start times

D. To monitor container CPU usage

Solution

1. Step 1: Understand Docker storage drivers

   Storage drivers define how Docker saves and manages container data on the host disk.

2. Step 2: Identify the correct function

   Among the options, only managing container data storage matches the role of storage drivers.

3. Final Answer:

   To manage how Docker stores container data on disk -> Option A

4. Quick Check:

   Storage driver = manages container data storage [OK]

Hint: Storage drivers handle container data storage, not networking or CPU [OK]

Common Mistakes:

• Confusing storage drivers with network drivers
• Thinking storage drivers manage container resource limits
• Assuming storage drivers schedule container tasks

2. Which of the following is the correct syntax to specify the storage driver when starting the Docker daemon manually?

easy

A. docker run --storage-driver=overlay2

B. dockerd --storage-driver=overlay2

C. dockerd -storage driver overlay2

D. docker daemon --storage=overlay2

Solution

1. Step 1: Recall Docker daemon start syntax

   The Docker daemon is started with the command 'dockerd' and options use double dashes with hyphens.

2. Step 2: Match correct option format

   dockerd --storage-driver=overlay2 uses 'dockerd --storage-driver=overlay2' which is the correct syntax to set the storage driver.

3. Final Answer:

   dockerd --storage-driver=overlay2 -> Option B

4. Quick Check:

   Daemon start uses 'dockerd --storage-driver' [OK]

Hint: Use 'dockerd --storage-driver=drivername' to set storage driver [OK]

Common Mistakes:

• Using 'docker run' instead of 'dockerd' to set storage driver
• Incorrect flag syntax like '-storage driver'
• Using 'docker daemon' which is deprecated

3. Given the Docker daemon started with dockerd --storage-driver=aufs, what will be the output of docker info | grep 'Storage Driver'?

medium

A. Storage Driver: aufs

B. Storage Driver: btrfs

C. Storage Driver: devicemapper

D. Storage Driver: overlay2

Solution

1. Step 1: Understand the command effect

   The command 'docker info | grep "Storage Driver"' filters Docker info output to show the storage driver in use.

2. Step 2: Match the storage driver set at daemon start

   Since the daemon was started with '--storage-driver=aufs', the output will show 'Storage Driver: aufs'.

3. Final Answer:

   Storage Driver: aufs -> Option A

4. Quick Check:

   Set driver = output driver [OK]

Hint: Output matches the driver set at daemon start [OK]

Common Mistakes:

• Assuming default driver instead of the one set
• Confusing output with other storage drivers
• Not using correct grep syntax

4. You tried to start Docker with dockerd --storage-driver=overlay3 but it failed. What is the most likely reason?

medium

A. The storage driver option requires a space, not an equals sign

B. You need to use 'docker run' instead of 'dockerd'

C. Docker does not support storage drivers on Linux

D. overlay3 is not a valid Docker storage driver

Solution

1. Step 1: Verify valid storage drivers

   Docker supports drivers like overlay2, aufs, devicemapper, but 'overlay3' is not a valid driver.

2. Step 2: Check command usage

   The command 'dockerd --storage-driver=overlay3' is correct syntax, but the driver name is invalid, causing failure.

3. Final Answer:

   overlay3 is not a valid Docker storage driver -> Option D

4. Quick Check:

   Invalid driver name causes failure [OK]

Hint: Check driver name spelling and validity before starting daemon [OK]

Common Mistakes:

• Using invalid or unsupported driver names
• Confusing 'dockerd' with 'docker run'
• Incorrect flag syntax

5. You want to optimize Docker performance on a system with an ext4 filesystem. Which storage driver option should you choose in the Docker daemon configuration file for best compatibility and performance?

hard

A. aufs

B. devicemapper

C. overlay2

D. btrfs

Solution

1. Step 1: Identify filesystem compatibility

   Overlay2 is recommended for ext4 filesystems because it is stable and performs well on ext4.

2. Step 2: Compare other drivers

   Devicemapper is older and less efficient; aufs is deprecated on many systems; btrfs requires btrfs filesystem, not ext4.

3. Final Answer:

   overlay2 -> Option C

4. Quick Check:

   ext4 + overlay2 = best performance [OK]

Hint: Use overlay2 for ext4 filesystem for best Docker performance [OK]

Common Mistakes:

• Choosing btrfs on ext4 filesystem
• Using devicemapper despite better options
• Assuming aufs is always best