Object Store¶
Introduction¶
Chameleon provides an object store service through the OpenStack Swift interface. It is intended to be used for storing and retrieving data used during experiments, such as input files needed for your applications, or results produced by your experiments.
Hint
Chameleon object store service is currently backed by a Ceph cluster with more than 2.1 PB of capacity. The data is replicated, keeping two copies of each object, effectively providing over 1 PB of storage available to users. This storage capacity will increase as the project goes on. The replication should provide good availability in case of hardware failures. However, all copies are kept within the same data center and are not backed up on a separate system; if you feel that this does not provide sufficient reliability in your case, you should consider backing up really critical data externally.
Availability¶
You can access the Object Store from instances running on CHI@TACC and CHI@UC. Each region has its own store, meaning that objects uploaded to one are not visible to the other. In general you should use the store local to the region where your instances are running for the best performance. To make it easier for you to use the Object Store client, we installed it in all appliances supported by Chameleon. Additionally, you can also access the Object Store from the CHI@TACC or CHI@UC web interfaces under the Object Store panel.
Hint
KVM@TACC users can access the TACC store by using their CHI@TACC OpenStack RC file.
Objects and Containers¶
Objects are equivalent to individual files. They are stored in Containers, which are data structures that can contain multiple Objects. When uploading Objects, they must be stored inside of Containers. You may perform operations on individual Objects inside Containers, such as downloading or deleting them. You may also work with entire Containers and perform operations such as downloading an entire Container.
Managing Object Store using the GUI¶
Note
The Object Store is implemented at TACC. Therefore, only CHI@TACC implements a GUI interface for the Object Store. However, the CLI works for both CHI@TACC and CHI@UC.
To access the Object Store using the GUI at CHI@TACC, use the navigation sidebar to go to Project > Object Store > Containers.
The Containers page
Working with Containers¶
To create a container, click the +Container button. This will open the Create Container dialog.
The Create Container dialog
Choose a unique name of your container and set the visibility to either Public or Not Public. When you are finished, click the Submit button. You will see your new Container appear in the list on the Containers page.
The Container list
You may click on a Container to see the details and work with Objects belong to it.
Container details
Attention
Downloading a container is not available from the GUI. Use the CLI to download containers.
You may delete a container by clicking the Delete icon in the upper right of the Container Detail Panel.
The Delete Container button
Working with Objects¶
To upload a local file to a container, click the button with the Upload symbol next to the search bar.
The Upload button
This will open the Upload File dialog.
The Upload File dialog
Choose a file to upload from your local file system and give a name to the object.
Working with Folders¶
If you wish to create a Folder within your Container, click the +Folder button and give a name to your folder in the Create Folder dialog.
The Create Folder dialog
Your new folder will appear in the Container details.
A Container with a Folder
You may browse your folder and upload files to it by clicking on the folder.
A Folder within the Container
Managing Object Store using the CLI¶
Tip
Reading The Command Line Interface is highly recommanded before continuing on the following sections.
In addition to Installing the CLI, you must also install python-swiftclient package:
pip install python-swiftclient
Then, you must set environment variables for your account and project using The OpenStack RC Script.
Working with Containers¶
To create a Container, use the following command:
swift post <container_name>
Tip
By default, the Container created using the above command will not be visible to the public.
To view all containers that belong to your project, run:
swift list
Tip
You may use --prefix <prefix> as a filter to list the containers whose name starts with <prefix>.
To see details of a container, use the command:
swift stat <container_name>
To view a list of objects within a container, use the command:
swift list <container_name>
To download a container with all the objects belong to it, use the following command:
swift download <container_name>
To delete a container and wipe out all the objects belong to it, use the following command:
swift delete <container_name>
Working with Objects¶
Tip
swift can upload objects up to 4GB. Larger objects must be broken into segments no larger than this with the –segment-size option indicating size in bits. --segment-size 4831838208 is close to 4GB and not above this limit.
You may upload a file from your local machine to a container using the following command:
swift upload <container_name> <local_filename>
Tip
Optionally, you may name the object differently from it’s original name in your local machine by using the --object-name <object_name> parameter.
To delete an object from a container, run:
swift delete <container_name> <object_name>
If you wish to download an individual object directly from a container, use the command:
swift download <container_name> <object_name>
Working with Folders¶
There isn’t “folders” when you managing the Object Store with the CLI. However, when you create an object, you may use the delimiter / to specify the path.
Mounting Object Store as a File System¶
Tip
Cloudfuse can upload objects up to 4GB. For larger objects, please use the Swift CLI.
When logged into an instance using Chameleon-supported images, such as CC-CentOS8 and CC-Ubuntu18.04,
you will see a directory called my_mounting_point which is a pre-mounted directory to your Chameleon Object Store at the same site of your instance. Each Object Store container that you have access to will appear as a subdirectory inside this mount.
The cc-cloudfuse tool (Source: ChameleonCloud/cc-cloudfuse) is pre-installed in Chameleon-supported images.
It is based on the cloudfuse tool (Source: redbo/cloudfuse), which is used to mount your Chameleon Object Store as a directory on your Linux environment.
To mount, use the following command:
cc-cloudfuse mount <mount_dir>
Now you can access your Chameleon Object Store as your local file system.
To unmount, use the following command:
cc-cloudfuse unmount <mount_dir>
Important
Limitations
The primary usage scenario of the cc-cloudfuse tool is to allow you to interact with Chameleon Object Store using familiar file system operations.
Because the cc-cloudfuse runs on top of an object store, it is important to understand that not all functionality will behave identically to a regular file system.
- Symbolic links, file permissions, and POSIX file locking operations are not supported.
- Updating an existing file is an expensive operation as it downloads the entire file to local disk before it can modify the contents.
- You can mount from multiple nodes, but there is no synchronization between nodes regarding writes to Object Storage.
- The mounting root directory can only contain directories, as they are mapped to Object Store containers.
- Renaming directories is not allowed.
- It keeps an in-memory cache of the directory structure, so it may not be usable for large file systems. In addition, files added by other applications will not show up until the cache expires.
- The maximum number of listings is 10,000 items.
Please keep these limitations in mind when evaluating cc-cloudfuse.
Note
You may experience persistence issues when using cc-cloudfuse, especially when writing large files or writing many files at the same time. Unmounting and re-mounting usually resolves this.