In Kubernetes, managing storage is a key element, especially when you need to handle stateful applications. Two concepts that are often misunderstood are volumeDevices and volumeMounts . Both play crucial roles in connecting containerized applications to storage. Understanding the differences between these two will help users deploy and manage Kubernetes applications effectively.

Overview of volumeDevices

and volumeMounts

volumeMounts

volumeMounts is the traditional way of mounting persistent storage into containers in Kubernetes. It’s typically used for mounting filesystem-backed volumes and provides a directory into the container's filesystem, where the application can interact with the data:

• name: app-container
  • mountPath: /data
• name: app-storage
• mountPath : The directory path inside the container where the volume is mounted.
• name : Refers to the volume specified within the pod’s volumes array.
  • name: app-container
    • devicePath: /dev/xvda
  • name: block-storage
• devicePath : Specifies the path in the container to expose the block device.
• name : Like volumeMounts , it links to a volume declaration in the pod specification.
• Standard Applications: Most applications that require file-based storage will benefit from volumeMounts . This is especially true for any application that writes or reads files, such as web servers storing media files or databases saving binary logs.
• POSIX Compliance: Since volumeMounts allows files to be accessed and manipulated using standard file system calls, it adheres to POSIX standards, making it ideal for applications expecting this behavior.
• Low-level Storage Interfaces: Some applications, like database engines that manage their own storage layers or applications that write data directly to block devices for performance reasons, can make efficient use of volumeDevices .
• Performance: Direct block storage allows applications to bypass the overhead associated with a filesystem, potentially improving I/O performance, crucial for high-performance computing applications.
• Complexity: Using volumeDevices can introduce complexity, as applications now need to handle block device operations, which can be non-trivial and error-prone.
• Compatibility: Not all applications are suited to handle raw block devices - transitioning an application to use volumeDevices when designed for filesystem access can require significant engineering effort.