Comparison between OSS and file systems - Object Storage Service

This topic provides a side-by-side comparison of Object Storage Service (OSS) with file systems to help you better understand the concepts and differences.

Comparison

The following table compares OSS with file systems in terms of data models, data retrieval methods, advantages, and disadvantages.

Item	OSS	File system
Data model	OSS is a distributed object storage service that stores data as key-value pairs.	A file system uses a tree structure for directory indexing.
Data retrieval method	Objects in OSS are retrieved based on object names, which are also referred to as keys. OSS uses a flat structure to store objects. For example, an object named `test1/test.jpg` does not mean that the object is stored in the test1 directory. In OSS, `test1/test.jpg` is a string that is not essentially different from example.jpg. Requests for objects that have different names consume similar resources.	To access a file named `test1/test.jpg`, you must first access the test1 directory and then obtain the test.jpg file from the directory.
Advantages	OSS supports a high number of concurrent operations.	Files can be modified. For example, a file can be modified at a specified offset or truncated from the end. Folder operations are supported. For example, a folder can be renamed, moved, or deleted.
Disadvantages	Objects in OSS cannot be modified. Object content changes involve calling of a specific API operation and the generated objects have a different type from objects that are normally uploaded. You need to re-upload the entire object even if one byte of the object is modified. OSS supports operations on simulated directories at considerable costs. For example, when you rename a directory from test1 to test2, OSS creates a copy of all the objects whose names have the `test1/` prefix and renames the copies so that their names are prefixed with `test2/`. This operation takes time and consumes a large number of bandwidth, storage, and computing resources. We recommend that you do not perform such operations.	The performance of a file system is limited by the performance of the device where the file system resides. Accessing files in deeper directories consumes more resources and requires longer time.

We recommend that you do not use OSS as a file system. If you must use OSS as a file system, we recommend that you only perform read, write, and delete operations for efficiency. You can make full use of OSS advantages, such as the capability to process and store large amounts of unstructured data such as images, videos, and documents.

Terminology

The following table describes the terminologies and operations in OSS and their equivalents in file systems.

OSS	File system
object	file
bucket	home directory
region	N/A
endpoint	N/A
AccessKey	N/A
N/A	multilevel directory
GetService	obtain the list of home directories
GetBucket	Obtain the list of files
PutObject	create a file
AppendObject	append data to an existing file
GetObject	read a file
DeleteObject	delete a file
N/A	modify file content
CopyObject (same source and destination objects)	modify file attributes
CopyObject (different source and destination objects)	Copy a file
Rename	rename a file