accelerated-container-image | accelerated-container-image | File Utils library

accelerated-container-image is a Go library typically used in Utilities, File Utils applications. accelerated-container-image has no bugs, it has no vulnerabilities, it has a Permissive License and it has low support. You can download it from GitHub.

With OCI image spec, an image layer blob is saved as a tarball on the registry, describing the changeset based on it's previous layer. However, tarball is not designed to be seekable and random access is not supported. Complete downloading of all blobs is always necessary before bringing up a container. An overlaybd blob is a collection of modified data blocks under the filesystem and corresponding to the files added, modified or deleted by the layer. The overlaybd backstore is used to provide the merged view of layers and provides a virtual block device. Filesystem is mounted on top of the device and an overlaybd blob can be accessed randomly and supports on-demond reading natively. The raw data of block differences, together with an index to the raw data, constitute the overlaybd blob. When attaching and mounting an overlaybd device, only indexes of each layer are loaded from remote, and stored in memory. For data reading, overlaybd performs a range lookup in the index to find out where in the blob to read and then performs a remote fetching. That blob is in Zfile format. Zfile is a new compression file format to support seekable decompression, which can reduce storage and transmission costs. And also the checksum information to protect against data corruptions for on-demand reading is stored in Zfile. In order to be compatible with existing registries and container engines, Zfile is wrapped by a tar file, which has only one Zfile inside. Overlaybd connects with applications through a filesystem mounted on an virtual block device. Overlaybd is agnostic to the choice of filesystem so users can select one that best fits their needs. I/O requests go from applications to a regular filesystem such as ext4. From there they go to the loopback iSCSI device (through TCM_loopback) and then to the user space overlaybd backstore (through TCMU). Backend read operations are always on layer files. Some of the layer files may have already been downloaded, so these reads would hit local filesystem. Other reads will be directed to registry, or hit the registry cache. Write and trim operations are handled by overlaybd backstore which writes the data and index files of the writable layer to the local file system. For more details, see the paper.