VxRail systems leverage VMware’s vSAN software, which is fully integrated with vSphere and provides full-featured and cost-effective software-defined storage. vSAN implements a notably efficient architecture, built directly into hypervisor. This distinguishes vSAN from solutions that typically install a virtual storage appliance (VSA) that runs as a guest VM on each host. Embedding vSAN into the ESXi kernel layer has obvious advantages in performance and memory requirements. It has very little impact on CPU utilization (less than 10 percent) and self-balances based on workload and resource availability. It presents storage a familiar datastore construct and works seamlessly with other vSphere features such as vMotion.
vSAN aggregates locally attached disks of hosts in a vSphere cluster to create a pool of distributed shared storage. Capacity is easily scaled up by adding additional disks to hosts in the cluster and scaled out by adding additional ESXi hosts. This provides the flexibility to start with a very small environment and scale it over time. Storage characteristics are configured using Storage Policy Based Management (SPBM), which allows object-level policies to be set and modified on the fly to control storage provisioning and day-to-day management of storage service-level agreements (SLAs). vSphere and vSAN provide the foundation for VxRail performance and scale, and enable enterprise-class capabilities for hosted virtual machines including mobility using vMotion, High Availability, and Dynamic Resource Scheduler (DRS).
vSAN is preconfigured when the VxRail system is first initialized and managed through vCenter. The VxRail system-initialization process discovers locally attached storage disks from each ESXi node in the cluster to create a distributed, shared-storage datastore. The amount of storage in the vSAN datastore is an aggregate of all of the capacity drives in the cluster.
The figure below shows an example of a hybrid configuration where each node contributes storage capacity to the vSAN datastore. The SSD drive provides caching to optimize performance and hard disk drives (HDD) for capacity.
Figure 41. vSAN datastore
vSAN enables rapid storage provisioning within vCenter as part of the VM-creation and deployment operations. vSAN is policy driven and designed to simplify storage provisioning and management. It automatically and dynamically matches requirements with underlying storage resources based on VM-level storage policies. VxRail provides two different vSAN node-storage configuration options: a hybrid configuration that leverages both flash SSDs and mechanical HDDs, and an all-flash SSD configuration. The hybrid configuration uses flash SSDs at the cache tier and mechanical HDDs for capacity and persistent data storage. The all-flash configuration uses flash SSDs for both the caching tier and capacity tier.