Storage driver options in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Docker storage driver?

A Docker storage driver manages how images and containers store and share data on the host system's filesystem.

beginner

Name two common Docker storage drivers.

Overlay2 and aufs are two common Docker storage drivers used to manage container file systems.

intermediate

Why might you choose the overlay2 storage driver over aufs?

Overlay2 is preferred because it is simpler, faster, and supported by most modern Linux kernels, while aufs may require extra setup.

intermediate

How do you specify a storage driver when starting the Docker daemon?

You specify it with the --storage-driver option in the Docker daemon configuration or command line, for example: dockerd --storage-driver=overlay2

advanced

What happens if you change the Docker storage driver on an existing system?

Changing the storage driver can cause existing images and containers to become unusable because each driver uses a different format for storing data.

Which Docker storage driver is recommended for most modern Linux systems?

A devicemapper

B btrfs

C overlay2

D vfs

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

What command option sets the storage driver for the Docker daemon?

A --storage

B --driver-storage

C --driver

D --storage-driver

The correct option is --storage-driver to specify which storage driver Docker should use.

What is a risk of switching storage drivers on a Docker host with existing containers?

A Containers may stop working due to incompatible storage formats

B Docker will automatically migrate all data safely

C No impact, containers continue as normal

D Docker will delete all images automatically

Switching storage drivers can break existing containers because each driver stores data differently.

Which storage driver uses a copy-on-write mechanism to save space?

A overlay2

B vfs

C devicemapper

D none

Overlay2 uses copy-on-write to efficiently share files between containers.

If your Linux kernel does not support overlay2, which driver might you use?

A vfs

B aufs

C zfs

D overlay2

Aufs is an alternative storage driver used when overlay2 is not supported by the kernel.

Explain what a Docker storage driver does and why it matters.

Think about how Docker saves container data on your computer.

Describe the steps to change the Docker storage driver and what precautions you should take.

Changing storage drivers is like changing how your files are saved; it needs care.

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