Add doc: How to Setup Object Storage (#135)

* Add doc: How to Setup Object Storage

* Update

* Update

* Add IAM role

* Update

README.md

@@ -69,15 +69,7 @@ It will create a volume with default settings. If there Redis server is not runn
 
 As JuiceFS relies on object storage to store data, you can specify a object storage using `--storage`, `--bucket`, `--access-key` and `--secret-key`. By default, it uses a local directory to serve as an object store, for all the options, please see `./juicefs format -h`.
 
-To use MinIO as object store, it could be specified as:
-
-```bash
-$ ./juicefs format --storage minio \
-   --bucket http://1.2.3.4:9000/mybucket \
-   --access-key XXX \
-   --secret-key XXX \
-   localhost test
-```
+For the details about how to setup different object storage, please read [the guide](docs/how_to_setup_object_storage.md).
 
 ### Mount a volume
 

README_CN.md

@@ -70,15 +70,7 @@ $ ./juicefs format localhost test
 
 JuiceFS 还需要一个对象存储，可以通过参数 `--storage`、`--bucket`、`--access-key` 和 `--secret-key` 来指定。它默认会使用本地目录来模拟一个对象存储用于测试，详细的参数请看 `./juicefs format -h`。
 
-如果使用 MinIO 来存数据，可以这么写：
-
-```bash
-$ ./juicefs format --storage minio \
-   --bucket http://1.2.3.4:9000/mybucket \
-   --access-key XXX \
-   --secret-key XXX \
-   localhost test
-```
+关于各种对象存储如何设置的详细介绍，请查看[这个文档](docs/how_to_setup_object_storage.md)。
 
 ### 挂载
 

docs/how_to_setup_object_storage.md

@@ -0,0 +1,52 @@
+# How to Setup Object Storage
+
+This is a guide about how to setup object storage when format a volume. Different object storage may has different option value. Check the specific object storage for your need.
+
+## Access key and secret key
+
+For authentication, the access key and secret key are needed. You could specify them through `--access-key` and `--secret-key` options. Or you can set `ACCESS_KEY` and `SECRET_KEY` environment variables.
+
+Public cloud provider usually allow user create IAM (Identity and Access Management) role (e.g. [AWS IAM role](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles.html)) or similar thing (e.g. [Alibaba Cloud RAM role](https://help.aliyun.com/document_detail/93689.html)), then assign the role to VM instance. If your VM instance already have permission to access object storage, then you could omit `--access-key` and `--secret-key` options.
+
+## S3
+
+S3 supports [two style URI](https://docs.aws.amazon.com/AmazonS3/latest/dev/VirtualHosting.html): virtual hosted-style and path-style. The difference between them is:
+
+- Virtual hosted-style: `https://<bucket>.s3.<region>.amazonaws.com`
+- Path-style: `https://s3.<region>.amazonaws.com/<bucket>`
+
+The `<region>` should be replaced with specific region code, e.g. the region code of US East (N. Virginia) is `us-east-1`. You could find all available regions at [here](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-regions-availability-zones.html#concepts-available-regions).
+
+***Note: For AWS China user, you need add `.cn` to the host, i.e. `amazonaws.com.cn`. And check [this document](https://docs.amazonaws.cn/en_us/aws/latest/userguide/endpoints-arns.html) to know your region code.***
+
+Currently, **JuiceFS only supports virtual hosted-style** and maybe support path-style in the future ([#134](https://github.com/juicedata/juicefs/issues/134)). So when you format a volume, the `--bucket` option should be virtual hosted-style URI. For example:
+
+```bash
+$ ./juicefs format \
+    --storage s3 \
+    --bucket https://<bucket>.s3.<region>.amazonaws.com \
+    ... \
+    localhost test
+```
+
+You can also use S3 storage type to connect S3-compatible storage. But beware that you still need use virtual hosted-style URI. For example:
+
+```bash
+$ ./juicefs format \
+    --storage s3 \
+    --bucket https://<bucket>.<endpoint> \
+    ... \
+    localhost test
+```
+
+## MinIO
+
+[MinIO](https://min.io) is an open source high performance object storage. It is API compatible with Amazon S3. You need set `--storage` option to `minio`. Currently, JuiceFS only supports path-style URI when use MinIO storage. For example (`<endpoint>` may looks like `1.2.3.4:9000`):
+
+```bash
+$ ./juicefs format \
+    --storage minio \
+    --bucket http://<endpoint>/<bucket> \
+    ... \
+    localhost test
+```