VMware Virtual SAN (VSAN)

At VMworld 2013 in San Francisco, VMware announced the beta version of VMware Virtual SAN (VSAN). Primarily, it allows the use of local hard drives and solid state drives (SSDs) to be utilized to provide shared storage to support vSphere features that typically involve a SAN. It also allow the use of policies to be assigned to VMs to simplify storage management. Here are some details.

vSAN uses direct attached SSD and spinning disk storage to create shared storage suitable for vMotion, DRS, and HA.
The local SSDs provide read / write cache for the spinning disks.
It utilizes VM storage policies to ensure the performance and availability SLA’s of each VM are met.
It provides policies such as number of host failures to tolerate, number of disk stripes per object, and read flash cache reservation.
It utilizes pass-through mode (HBA mode) of SAS and SATA controllers to allow VSAN to manage RAID based on VM policies.
It utilizes an additional vmkernel port labeled Virtual SAN.
It can be enabled at the cluster level, just like DRS and HA. It is not limited to 3 hosts, although the legacy virtual storage appliance is.
It allows the increase of the shared storage space by simply adding more hosts to the cluster
It can automatically discover the disks and SSD in each host and automatically configure the storage. Or the administrator can manually configure.

For more details see Whats New in VMware VSAN.