vSAN for Rackspace Private Cloud powered by VMware (RPC-VMware) contains the following components.
|Host||ESXi hosts (hypervisors) run the vSAN software and provide the local drives that are used for the cache and capacity tiers.|
|Disk group||A disk group is a unit of physical storage capacity on a host and a group of physical devices that provide performance and capacity to the vSAN cluster. On each ESXi host that contributes its local devices to a vSAN cluster, devices are organized into disk groups.|
|Capacity tier||The capacity tier is used to permanently store data that is stored in vSAN. Cold data not in the cache tier is written to the capacity tier. The capacity tier is made up of flash disks.|
|Cache tier or flash cache||
Each disk group must have one flash cache device and one or more capacity devices. The devices used for caching cannot be shared across disk groups, and cannot be used for other purposes. A single caching device must be dedicated to a single disk group.
RPC-VMware uses only all-flash clusters. In an all-flash cluster, flash devices are used for both the cache tier and capacity tier. In all-flash clusters, the cache tier is used to cache writes only.
|vSAN datastore||The datastore that is provided by vSAN and backed by the aggregate storage of all drives claimed by vSAN.|
|VM storage policy||VM-level availability and performance policies that can be set and modified as needed. vSAN works with VM storage policies to support a VM-centric storage approach. If no storage policy is explicitly assigned to a VM is when it is provisioned, a generic system-defined storage policy called the vSAN Default Storage Policy is automatically applied to the VM.|
|Deduplication and compression||Deduplication and compression occur when data is destaged from the cache tier to the capacity tier. This function is set when you enable “space efficiency” on a cluster level. Deduplication happens on a per disk group basis. Bigger disk groups result in a higher deduplication ratio. After the blocks are deduplicated, they are compressed.|