General compute cloud¶

Storage requirements¶

Using a scale-out storage solution with direct-attached storage (DAS) in the servers is well suited for a general purpose OpenStack cloud. Cloud services requirements determine your choice of scale-out solution. You need to determine if a single, highly expandable and highly vertical, scalable, centralized storage array is suitable for your design. After determining an approach, select the storage hardware based on this criteria.

This list expands upon the potential impacts for including a particular storage architecture (and corresponding storage hardware) into the design for a general purpose OpenStack cloud:

Connectivity

If storage protocols other than Ethernet are part of the storage solution, ensure the appropriate hardware has been selected. If a centralized storage array is selected, ensure that the hypervisor will be able to connect to that storage array for image storage.

Usage

How the particular storage architecture will be used is critical for determining the architecture. Some of the configurations that will influence the architecture include whether it will be used by the hypervisors for ephemeral instance storage, or if OpenStack Object Storage will use it for object storage.

Instance and image locations

Where instances and images will be stored will influence the architecture.

Server hardware

If the solution is a scale-out storage architecture that includes DAS, it will affect the server hardware selection. This could ripple into the decisions that affect host density, instance density, power density, OS-hypervisor, management tools and others.

A general purpose OpenStack cloud has multiple options. The key factors that will have an influence on selection of storage hardware for a general purpose OpenStack cloud are as follows:

Capacity

Hardware resources selected for the resource nodes should be capable of supporting enough storage for the cloud services. Defining the initial requirements and ensuring the design can support adding capacity is important. Hardware nodes selected for object storage should be capable of support a large number of inexpensive disks with no reliance on RAID controller cards. Hardware nodes selected for block storage should be capable of supporting high speed storage solutions and RAID controller cards to provide performance and redundancy to storage at a hardware level. Selecting hardware RAID controllers that automatically repair damaged arrays will assist with the replacement and repair of degraded or deleted storage devices.

Performance

Disks selected for object storage services do not need to be fast performing disks. We recommend that object storage nodes take advantage of the best cost per terabyte available for storage. Contrastingly, disks chosen for block storage services should take advantage of performance boosting features that may entail the use of SSDs or flash storage to provide high performance block storage pools. Storage performance of ephemeral disks used for instances should also be taken into consideration.

Fault tolerance

Object storage resource nodes have no requirements for hardware fault tolerance or RAID controllers. It is not necessary to plan for fault tolerance within the object storage hardware because the object storage service provides replication between zones as a feature of the service. Block storage nodes, compute nodes, and cloud controllers should all have fault tolerance built in at the hardware level by making use of hardware RAID controllers and varying levels of RAID configuration. The level of RAID chosen should be consistent with the performance and availability requirements of the cloud.

Network hardware requirements¶

For a compute-focus architecture, we recommend designing the network architecture using a scalable network model that makes it easy to add capacity and bandwidth. A good example of such a model is the leaf-spine model. In this type of network design, you can add additional bandwidth as well as scale out to additional racks of gear. It is important to select network hardware that supports port count, port speed, and port density while allowing for future growth as workload demands increase. In the network architecture, it is also important to evaluate where to provide redundancy.

Network software requirements¶

For a general purpose OpenStack cloud, the OpenStack infrastructure components need to be highly available. If the design does not include hardware load balancing, networking software packages like HAProxy will need to be included.