Parallels Cloud Storage Architecture

Before starting the deployment process, you should have a clear idea of the Parallels Cloud Storage infrastructure. A typical Parallels Cloud Storage is shown below.

The basic component of Parallels Cloud Storage is a cluster. The cluster is a group of physical computers connected to the same Ethernet network and performing the following roles:

• chunk servers
• metadata servers
• client computers (or clients )

Brief Overview

All data in a Parallels Cloud Storage cluster, including Parallels virtual machine and Container disk images, is stored in the form of fixed-size chunks on chunk servers. The cluster automatically replicates the chunks and distributes them across the available chunk servers to provide high availability of data.

To keep track of data chunks and their replicas, the cluster stores metadata about them on metadata (MDS) servers. The central MDS server, called the master MDS server , monitors all cluster activity and keeps metadata current.

Clients manipulate data stored in the cluster by sending different types of file requests, such as modifying an existing file or creating a new one.

Chunk Servers

Chunk servers store all the data, including the contents of virtual machines and Containers, in the form of fixed-size chunks and provide access to these chunks. All data chunks are replicated and the replicas are kept on different chunk servers to achieve high availability. If one of the chunk servers goes down, the other chunk servers will continue providing the data chunks that were stored on the failed server.

Metadata Servers

Metadata (MDS) servers store metadata about chunk servers and control how files keeping the contents of virtual machines and Containers are split into chunks and where these chunks are located. MDS servers also ensure that a cluster has enough chunk replicas and store a global log of all important events that happen in the cluster.

To provide high availability for a Parallels Cloud Storage cluster, you need to set up several MDS servers in the cluster. In this case, if one MDS server goes offline, another MDS server will continue keeping control over the cluster.

Note: MDS servers deal with processing metadata only and do not normally participate in any read/write operations related to data chunks.

Clients

Clients are computers with Parallels Cloud Server 6.0 from where you run virtual machines and Containers stored in a Parallels Cloud Storage cluster.

Notes:

1. You can set up any computer in the cluster to perform the role of a metadata server, chunk server, or client. You can also assign two or all three roles to one and the same computer. For example, you can configure a computer to act as a client by installing Parallels Cloud Server 6.0 on it and running virtual machines and Containers from the computer. At the same time, if you want this computer to allocate its local disk space to the cluster, you can set it up as a chunk server.

2. Though Parallels Cloud Storage can be mounted as a file system, it is not a POSIX-compliant file system and lacks some POSIX features like ACL, user and group credentials, hardlinks, and some other.