distribution/docs/storagedrivers.md

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title = "Docker Registry Storage Driver"
description = "Explains how to use the storage drivers"
keywords = ["registry, service, driver, images, storage"]
[menu.main]
parent="smn_registry_ref"
identifier="smn_registry_drivers"
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<![end-metadata]-->
# Docker Registry Storage Driver
This document describes the registry storage driver model, implementation, and explains how to contribute new storage drivers.
## Provided Drivers
This storage driver package comes bundled with several drivers:
- [inmemory](storage-drivers/inmemory.md): A temporary storage driver using a local inmemory map. This exists solely for reference and testing.
- [filesystem](storage-drivers/filesystem.md): A local storage driver configured to use a directory tree in the local filesystem.
- [s3](storage-drivers/s3.md): A driver storing objects in an Amazon Simple Storage Solution (S3) bucket.
- [azure](storage-drivers/azure.md): A driver storing objects in [Microsoft Azure Blob Storage](http://azure.microsoft.com/en-us/services/storage/).
Storage Driver: Ceph Object Storage (RADOS) This driver implements the storagedriver.StorageDriver interface and uses Ceph Object Storage as storage backend. Since RADOS is an object storage and no hierarchy notion, the following convention is used to keep the filesystem notions stored in this backend: * All the objects data are stored with opaque UUID names prefixed (e.g. "blob:d3d232ff-ab3a-4046-9ab7-930228d4c164). * All the hierarchy information are stored in rados omaps, where the omap object identifier is the virtual directory name, the keys in a specific are the relative filenames and the values the blob object identifier (or empty value for a sub directory). e.g. For the following hierarchy: /directory1 /directory1/object1 /directory1/object2 /directory1/directory2/object3 The omap "/directory1" will contains the following key / values: - "object1" "blob:d3d232ff-ab3a-4046-9ab7-930228d4c164" - "object2" "blob:db2e359d-4af0-4bfb-ba1d-d2fd029866a0" - "directory2" "" The omap "/directory1/directory2" will contains: - "object3" "blob:9ae2371c-81fc-4945-80ac-8bf7f566a5d9" * The MOVE is implemented by changing the reference to a specific blob in its parent virtual directory omap. This driver stripes rados objects to a fixed size (e.g. 4M). The idea is to keep small objects (as done by RBD on the top of RADOS) that will be easily synchronized accross OSDs. The information of the original object (i.e total size of the chunks) is stored as a Xattr in the first chunk object. Signed-off-by: Vincent Giersch <vincent.giersch@ovh.net>
2015-04-23 16:13:52 +00:00
- [rados](storage-drivers/rados.md): A driver storing objects in a [Ceph Object Storage](http://ceph.com/docs/master/rados/) pool.
## Storage Driver API
The storage driver API is designed to model a filesystem-like key/value storage in a manner abstract enough to support a range of drivers from the local filesystem to Amazon S3 or other distributed object storage systems.
Storage drivers are required to implement the `storagedriver.StorageDriver` interface provided in `storagedriver.go`, which includes methods for reading, writing, and deleting content, as well as listing child objects of a specified prefix key.
Storage drivers are intended to be written in Go, providing compile-time
validation of the `storagedriver.StorageDriver` interface.
## Driver Selection and Configuration
The preferred method of selecting a storage driver is using the `StorageDriverFactory` interface in the `storagedriver/factory` package. These factories provide a common interface for constructing storage drivers with a parameters map. The factory model is based off of the [Register](http://golang.org/pkg/database/sql/#Register) and [Open](http://golang.org/pkg/database/sql/#Open) methods in the builtin [database/sql](http://golang.org/pkg/database/sql) package.
Storage driver factories may be registered by name using the
`factory.Register` method, and then later invoked by calling `factory.Create`
with a driver name and parameters map. If no such storage driver can be found,
`factory.Create` will return an `InvalidStorageDriverError`.
## Driver Contribution
### Writing new storage drivers
To create a valid storage driver, one must implement the
`storagedriver.StorageDriver` interface and make sure to expose this driver
via the factory system.
#### Registering
Storage drivers should call `factory.Register` with their driver name in an `init` method, allowing callers of `factory.New` to construct instances of this driver without requiring modification of imports throughout the codebase.
## Testing
Storage driver test suites are provided in
`storagedriver/testsuites/testsuites.go` and may be used for any storage
driver written in Go. Tests can be registered using the `RegisterSuite`
function, which run the same set of tests for any registered drivers.