Storage driver options in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Identify the storage driver used by Docker

You run the command docker info to check Docker's storage driver. Which output line correctly shows the storage driver in use?

Docker

docker info

A Storage Driver: btrfs

B Storage Driver: aufs

C Storage Driver: overlay2

D Storage Driver: devicemapper

💡 Hint

Look for the line starting with 'Storage Driver:' in the output.

The 'docker info' command shows the current storage driver under the 'Storage Driver:' line. 'overlay2' is the default and most common on modern Linux systems.

❓ Configuration

intermediate

Configure Docker to use a specific storage driver

You want Docker to use the 'devicemapper' storage driver. Which configuration file and setting correctly applies this change?

A In /etc/docker/daemon.json, set {"driver": "devicemapper"}

B In /etc/docker/daemon.conf, set storage_driver=devicemapper

C In /etc/docker/config.json, set "driver": "devicemapper"

D In /etc/docker/daemon.json, set {"storage-driver": "devicemapper"}

💡 Hint

Docker daemon configuration uses JSON format in daemon.json.

The Docker daemon reads /etc/docker/daemon.json for configuration. The correct key to set the storage driver is 'storage-driver'.

❓ Troubleshoot

advanced

Troubleshoot Docker storage driver error on startup

Docker fails to start and logs an error about the storage driver 'aufs' not being supported. What is the most likely cause?

A The Linux kernel does not have aufs support enabled or installed

B The Docker daemon configuration file is missing

C The Docker client version is incompatible with the daemon

D The Docker image is corrupted

💡 Hint

Storage drivers depend on kernel modules.

The 'aufs' driver requires kernel support. If the kernel lacks aufs modules, Docker cannot use it and will fail to start with that error.

✅ Best Practice

advanced

Choose the best storage driver for production Docker on modern Linux

Which storage driver is recommended for most production Docker setups on modern Linux distributions?

A overlay2

B aufs

C devicemapper

D btrfs

💡 Hint

Consider stability, performance, and kernel support.

Overlay2 is the default and recommended driver for modern Linux kernels due to its performance and stability.

🧠 Conceptual

expert

Understand the impact of changing Docker storage driver

What happens to existing Docker images and containers if you change the storage driver in Docker's configuration and restart the daemon?

A Docker deletes all images and containers but keeps volumes intact

B Existing images and containers become inaccessible because storage formats differ

C Docker automatically converts all images and containers to the new storage driver format

D Nothing changes; images and containers remain usable without interruption

💡 Hint

Storage drivers use different ways to store data on disk.

Changing the storage driver changes how Docker stores images and containers. Existing data is not compatible and becomes inaccessible.

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