By being a Software Defined Storage VSAN uses Storage Policies to provide storage resources to virtual machines. These policy driven objects specify how much of storage resources will be able to be consumed, or will be granted, to certain VMs.
Policies can be created in vCenter Server under VM Storage Policies.
Select VSAN enabled cluster to which policies will be granted.
Next step is to create a new VM Storage Policy. A VM Storage Policy is a group of rules that define how storage resources will be consumed by virtual machines to which this policy will be assigned to.
Since, allegedly, different virtual machines will have different storage requirements more VM Storage Policies will be created.
Rule set deserves a few words to be spent on. As first select VSAN under Rules based on vendor-specific capabilities.
A whole set of rules will be available:
Number of disk stripes per object: The number of HDDs across which each replica of a storage object is striped. A value higher than 1 may result in better performance (for e.g. when flash read cache misses need to get serviced from HDD), but also results in higher use of system resources. Default value is 1, maximum value is 12.
Flash read cache reservation(%): Flash capacity reserved as flash read cache for the storage object. Specified as a percentage of the logical size of the object. To be used only for addressing read performance issues. Reserved flash capacity cannot be used by other objects. Unreserved flash is shared fairly among all objects. Default value is 0%. Maximum value is 100%.
Number of failures to tolerate: Defines the number of host, disk or network failures a object can tolerate. For n failures tolerated "n+1" copies of the object are created and "2n+1" hosts contributing storage are required. Default value is 1, maximum value is 3.
Force provisioning: If this option is set to "yes" the object will be provisioned even if the policy specified in the storage policy is not satisfiable with the resources currently available in the cluster. VSAN will try to bring the object into compliance if and when resources become available. Default value is NO.
Object space reservation (%): Percentage of the logical size of the storage object that will be reserved (thick provisioned) upon VM provisioning. The rest of the storage object is thin provisioned. Default value is 0%, maximum value is 100%.
Select the datastore to which these rules will be applied: vsanDatastore will be our choice.
VM Storage Policies can be applied to either already created VMs by going to All vCenter Actions->VM Storage Policies-> Manage VM Storage Policies.
Select desired storage policy then click Apply to disks.
VM Storage Policies can also be assigned to specific virtual machines during VM creation process.
You are now ready for the VSAN experience!!
Other blog posts in VSAN Series:
VSAN Part1 - Introduction
VSAN Part2 - Initial Setup
VSAN Part3 - Storage Policies
VSAN Part4 - Automate VSAN using PowerCLI