VSAN“VMware Virtual SAN abstracts and pools server-side flash and disk into shared pools of capacity with policy-based management and application-centric data services.”
Virtual SAN pools server-attached hard disk drives and flash (SSDs, and PCI-e) drives to create a distributed shared datastore that abstracts the storage hardware and provides a Software-Defined Storage (SDS) tier for virtual machines.
“VSAN leverages the power of any solid state drives (SSDs) on the hosts in the cluster for read caching and write buffering to improve performance."
In a hybrid architecture VSAN has both Flash (SSDs and PCI-e) and hard disk drive (HDD) devices. The Flash devices are utilized as a read cache and the HDDs are pooled to ceate a distributed shared datastore.
- Introduced with vSphere 5.5
- Creates Virtual SAN shared datastore
- Embedded in the hypervisor kernel
- Hybrid or all-Flash architecture
- Flash provides caching
- Managed via the vSphere Web Client
- Per-VM policies
- Minimum of three hosts per VSAN cluster
- Maximum of eight hosts per VSAN cluster
- Requires at least one VMkernel port per host
- One or more SSDs per host
- One or more HDDs per host
- Uses a proprietary protocol of IP over a VMKernel port to communicate between the nodes
- 1 Gbps network between hosts (10 Gbps recommended)
Caching: When blocks are written to the underlying datastore, they are first written to the SSDs, and later the data can be relocated to the HDDs.
VSAN uses "RAIN, or Reliable Array of Independent Nodes" instead of RAID. With RAIN, all the disks across all the hosts are combined into a large pool of storage. This storage is accessible across all the hosts in the cluster. RAIN enables HA across disk or host failures.
VSA (vSphere Storage Appliance) runs in a VM while VMware’s Virtual SAN (VSAN) is integrated into vSphere hypervisor (ESXi).
|vSphere Storage Appliance||VMware Virtual SAN|
|Description||Low cost, simple shared storage for small deployments||Scale-out distributed storage designed for virtualized/cloud environments|
|Form Factor||Virtual Appliance||Built into vSphere kernel|
|Scalability||2 to 3 vSphere servers
Does not scale beyond 3 hosts
|Minimum 3 node deployment
Scale out to 8 nodes
|Performance||No SSD requirement||SSD Caching requirement|
"VSAN employs algorithms to help protect against data loss, such as ensuring that the data exists on multiple participating VSAN nodes at the same time."
VSAN is conceptually similar to the VSA, however VSAN provides better scaling, does not require NFS mounts, is embedded into the hypervisor, thus eliminating the complexity of deploying and managing a virtual appliance.