Erofs Snapshotter Improvements

May 9, 2025 by ADMIN 31 views

Introduction

Erofs snapshotter is a feature that allows for efficient and reliable snapshotting of file systems in Kata Containers. As demonstrated in #11172, Kata already supports erofs snapshotter with virtio-blk. However, there are still some works we have yet to complete to fully utilize this feature. In this article, we will discuss the improvements needed for erofs snapshotter, including adding CI for the feature and supporting erofs flattened filesystem feature.

Add CI for Erofs Snapshotter Feature

To ensure the functionality of erofs snapshotter works correctly across various environments, we need to add Continuous Integration (CI) for this feature. Currently, the latest version of containerd used in Kata is 2.0, while erofs snapshotter feature is included starting from containerd 2.1. Therefore, we should consider upgrading the containerd version to 2.1. This will enable us to test and verify the erofs snapshotter feature in a more comprehensive manner.

Benefits of Upgrading Containerd Version

Upgrading the containerd version to 2.1 will provide several benefits, including:

Improved compatibility: With the latest version of containerd, we can ensure that our erofs snapshotter feature is compatible with the latest containerd releases.
Enhanced security: The latest version of containerd includes several security patches and updates that will improve the overall security of our erofs snapshotter feature.
Better performance: The latest version of containerd includes several performance enhancements that will improve the overall performance of our erofs snapshotter feature.

Support Erofs Flattened Filesystem Feature

The current implementation of erofs snapshotter uses one block device per layer, requiring each block device to be passed to the guest via virtio-blk. This results in a total of (number of block device mounts) + 1 mount operations, with the extra mount being the overlay mount. As described by @hsiangkao, erofs snapshotter will support a flattened filesystem feature, which supports to mount once for multiple layers to reduce the required mount operations.

Benefits of Flattened Filesystem Feature

The flattened filesystem feature will provide several benefits, including:

Improved performance: By reducing the number of mount operations, the flattened filesystem feature will improve the overall performance of our erofs snapshotter feature.
Simplified configuration: With the flattened filesystem feature, we can simplify the configuration of our erofs snapshotter feature, making it easier to use and manage.
Enhanced reliability: The flattened filesystem feature will improve the overall reliability of our erofs snapshotter feature, reducing the likelihood of errors and failures.

Example Use Cases

Here are some example use cases for the flattened filesystem feature:

Mounting multiple layers: With the flattened filesystem feature, we can mount multiple layers in a single mount operation, reducing the number of mount operations required.
Merging multiple layers: With the flattened filesystem feature, we can merge multiple layers into a single file, reducing both the number of block devices required and the number of mount operations required.

mount -t erofs xxx/meta.erofs -odevice=0/layer.erofs,device=1/layer.erofs,...,device=x/.erofs xxx/fs
mount -t overlay -olowerdir=xxx/fs,...

or even merge multiple layers into a single file to reduce both the number of block devices and the number of mount operations required.

mount -t erofs /dev/vdX (a merged virtual block device) filepath.Join(defaultKataGuestVirtualVolumedir, filename)
...

Conclusion

In conclusion, the erofs snapshotter feature is an important component of Kata Containers, and we need to continue improving it to ensure its functionality works correctly across various environments. By adding CI for the feature and supporting the erofs flattened filesystem feature, we can improve the overall performance, reliability, and simplicity of our erofs snapshotter feature. We will continue to work on these improvements and provide updates on our progress.

Previous Related Discussions

For more information on the erofs snapshotter feature and its improvements, please refer to the following related discussions:

https://github.com/kata-containers/kata-containers/pull/11172#discussion_r2075120589
Erofs Snapshotter Improvements: Q&A =====================================

Introduction

In our previous article, we discussed the improvements needed for erofs snapshotter, including adding CI for the feature and supporting erofs flattened filesystem feature. In this article, we will answer some frequently asked questions (FAQs) about erofs snapshotter improvements.

Q: What is erofs snapshotter?

A: Erofs snapshotter is a feature that allows for efficient and reliable snapshotting of file systems in Kata Containers. It uses the erofs file system to create snapshots of file systems, which can be used to create new file systems or to restore a file system to a previous state.

Q: Why do we need to add CI for erofs snapshotter feature?

A: We need to add CI for erofs snapshotter feature to ensure its functionality works correctly across various environments. Currently, the latest version of containerd used in Kata is 2.0, while erofs snapshotter feature is included starting from containerd 2.1. Therefore, we should consider upgrading the containerd version to 2.1 to test and verify the erofs snapshotter feature in a more comprehensive manner.

Q: What are the benefits of upgrading containerd version to 2.1?

A: Upgrading the containerd version to 2.1 will provide several benefits, including improved compatibility, enhanced security, and better performance.

Q: What is the flattened filesystem feature?

A: The flattened filesystem feature is a new feature in erofs snapshotter that supports to mount once for multiple layers to reduce the required mount operations. This feature will improve the overall performance of our erofs snapshotter feature.

Q: How will the flattened filesystem feature improve performance?

A: The flattened filesystem feature will improve performance by reducing the number of mount operations required. This will result in faster snapshot creation and restoration times.

Q: What are the benefits of the flattened filesystem feature?

A: The flattened filesystem feature will provide several benefits, including improved performance, simplified configuration, and enhanced reliability.

Q: Can you provide an example of how to use the flattened filesystem feature?

A: Yes, here are some example use cases for the flattened filesystem feature:

Mounting multiple layers: With the flattened filesystem feature, we can mount multiple layers in a single mount operation, reducing the number of mount operations required.
Merging multiple layers: With the flattened filesystem feature, we can merge multiple layers into a single file, reducing both the number of block devices required and the number of mount operations required.

mount -t erofs xxx/meta.erofs -odevice=0/layer.erofs,device=1/layer.erofs,...,device=x/.erofs xxx/fs
mount -t overlay -olowerdir=xxx/fs,...

or even merge multiple layers into a single file to reduce both the number of block devices and the number of mount operations required.

mount -t erofs /dev/vdX (a merged virtual block device) filepath.Join(defaultKataGuestVirtualVolumedir, filename)
...

Q: What is the next step for erofs snapshotter improvements?

A: The next step for erofs snapshotter improvements is to continue working on the flattened filesystem feature and to add CI for the feature. We will also continue to test and verify the erofs snapshotter feature in a more comprehensive manner.

Q: Where can I find more information on erofs snapshotter improvements?

A: You can find more information on erofs snapshotter improvements on the Kata Containers GitHub page. We will also provide updates on our progress and any new developments in the erofs snapshotter feature.