Introduction

If files are accidentally deleted from a file system, an application may be interrupted and the user data may be permanently lost. The trash can (also called "undelete" or "recycle bin") is a recommended feature in file systems that acts as a virtual trash can, allowing users to store deleted files temporarily before permanently deleting them. It provides a way to restore or retrieve deleted files if needed.

Once the trash can feature is enabled, when a user deletes a file from a file system, it is not actually deleted but moved to the trash can, deleted files and directories are temporarily stored in the trash can. The trash can may be manually emptied or once it is full, it will remove the oldest files first. Additionally, items in the trash can may be restored or retrieved if they are still there.

Trash Can/Undelete Functionalities

The trash can should including the following functionalities:

• List "undeleted" files in the trash can;
• After a file is deleted and moved into trash can, the quota for this file should be accounted and updated (reduced) accordingly;
• The trash can, and all files therein are not visible in the namespace of the file system;
• Restore a file in the trash can. This will restore a file to its original path. The corresponding quota account should be updated also;
• Delete a file in the trash can. This will finally remove the file from the file system and free the used space. The file is now unrecoverable;
• Empty the trash can. This will remove all files in the trash can;
• A user can restore files from trash can within the specified retention period. By this way, a file can be kept "undeleted" under a pre-defined configurable grace period.
• Enable/disable trash can feature on a entire file system;
• A administrator can enable/disable trash can feature on a specified directory;

Deleted files can no longer be restored from the trash can when:

• A file (or directory) is deleted again from the trash can. In other words it have been deleted twice. The first deletion only moves the file to the trash can. The second deletion actually removes the file from the file system.
• The trash can is emptied of all of its contents.

The Trash Can/Undelete HLD contains details of the design and implementation of this feature.