2.1. Storage architecture overview¶
The fundamental component of Acronis Cyber Infrastructure is a storage cluster: a group of physical servers interconnected by network. Each server in a cluster is assigned one or more roles and typically runs services that correspond to the following roles:
- Storage role: chunk service (CS)
- Metadata role: metadata service (MDS)
- Supplementary roles:
- SSD cache
- System
Any server in the cluster can be assigned a combination of storage, metadata, and supplementary roles.
Each cluster also requires that a web-based admin panel be installed on one (and only one) of the nodes. The panel enables administrators to manage the cluster.
2.1.1. Storage role¶
Storage nodes run chunk services, store all data 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 storage nodes to achieve high availability of data. If one of the storage nodes fails, the remaining healthy storage nodes continue providing the data chunks that were stored on the failed node.
The storage role can only be assigned to a server with disks of a certain capacity.
2.1.2. Metadata role¶
Metadata nodes run metadata services, store cluster metadata, and control how user files are split into chunks and where these chunks are located. Metadata nodes also ensure that chunks have the required amount of replicas. Finally, they log all important events that happen in the cluster.
To provide system reliability, Acronis Cyber Infrastructure uses the Paxos consensus algorithm. It guarantees fault-tolerance if the majority of nodes running metadata services are healthy.
To ensure high availability of metadata in a production environment, metadata services must be run on at least three cluster nodes. In this case, if one metadata service fails, the remaining two will still be controlling the cluster. However, it is recommended to have at least five metadata services to ensure that the cluster can survive simultaneous failure of two nodes and without data loss.
2.1.3. Supplementary roles¶
- SSD cache
- Boosts chunk read/write performance by creating write caches on selected solid-state drives (SSDs). It is also recommended to use such SSDs for metadata; refer to Metadata role for more information. The use of write journals may more than double the write speed in the cluster.
- System
- One disk per node that is reserved for the operating system and unavailable for data storage.