Before you activate Virtual SAN, verify that your environment meets all requirements.
Your environment must meet specific host and storage requirements. For networking requirements, see Virtual SAN Networking Requirements and Best Practices.
A minimum of three hosts contributing local disks is required. Each host must contribute one SSD and at least one HDD.
Install ESXi 5.5 or later on each host. You can add the hosts to the Virtual SAN cluster during initial setup of the cluster, or you can add hosts later.
The hosts must be managed by vCenter Server 5.5. Not all hosts need to have local storage. ESXi memory requirements: at least 6GB of RAM on each host.
Virtual SAN supports a limited number of storage devices, which are listed on the vSphere Compatibility Guide. Your environment must meet the following requirements.
One SAS or SATA or PCIe SSD. Make sure that Flash Read Cache does not use SSDs. Do not format SSDs with VMFS or any other file system.
One SAS or SATA Hard Disk (HDD). On each host, SSDs and HDDs are combined into disk groups. The capacity ratio of an SSD to HDDs typically depends on use cases and workloads, but the best practice is to use SSD capacity of at least 10 percent of the total consumed HDD capacity in each disk group, without counting the protection copies. For more information about disk groups, see Managing Disk Groups.
An SAS or SATA HBA, or RAID controller that is set up in RAID0 mode or passthrough.
The minimum memory requirement for one disk group is 6GB. For hosts with seven or more disks per a disk group, the memory requirement is 10GB or more. For more information about Virtual SAN memory requirement, see the Configuration Maximums documentation.
USB or SD Device Requirements for Persistent Logging
The minimum requirement for installing ESXi on USB or SD devices is a 4GB or larger USB or SD device. VMware recommends using a high quality USB flash drive of 16GB or larger. The extra space will be used for an expanded coredump partition on the USB or SD device.
If you allocate local storage to Virtual SAN, you might not have enough local disk or datastore left for persistent logging. To avoid this, configure the ESXi Dump Collector and Syslog Collector to redirect ESXi memory dumps and system logs onto a network server.
Due to the I/O sensitivity of USB and SD devices the installer does not create a scratch partition on these devices. When installing on USB or SD devices, the installer attempts to allocate a scratch region on an available local disk or datastore. If no local disk or datastore is found, /scratch is placed on the ramdisk. After the installation, you should reconfigure /scratch to use a persistent datastore. For more information about reconfiguring /scratch, see the vSphere Installation and Setup documentation.