VMware vSphere 7.x Study Guide for VMware Certified Professional – Data Center Virtualization certification. This article covers Section 1: Architectures and Technologies. Objective 1.3.3 – Describe storage policies
This article is part of the VMware vSphere 7.x - VCP-DCV Study Guide. Check out this page first for an introduction, disclaimer, and updates on the guide. The page also includes a collection of articles matching each objective of the official VCP-DCV.
Describe Storage Policies
Objective 1.3.3 is to describe storage policies. Here you can overview storage policy-based management (SPBM); which is the key topic within this objective. Virtual machines storage policies are also important to study, and good to know here (among other concepts) is virtual disk provisioning policies. Finally, you are also required to study vSAN storage policies.
Previous objective 1.3.2 is important before moving to this one. VASA provider is a key topic.
1. Storage Policy-Based Management (SPBM)
Within a software-defined data center, Storage Policy-Based Management (SPBM) plays a major role by helping to align storage with application demands of your virtual machines.
- SPBM provides a storage policy framework that serves as a single unified control panel across a broad range of data services and storage solutions.
- As an abstraction layer, SPBM abstracts storage services delivered by vVols, vSAN, I/O filters, or other storage entities.
- Rather than integrating with each individual type of storage and data services, SPBM provides a universal framework for different types of storage entities.
SPBM offers the following mechanisms:
- Advertisement of storage capabilities and data services that storage arrays and other entities, such as I/O filters, offer.
- Bidirectional communications between ESXi and vCenter Server on one side, and storage arrays and entities on the other.
- Virtual machine provisioning based on VM storage policies.
2. Virtual Machine Storage Policies
Virtual machine storage policies are essential to virtual machine provisioning through SPBM. The policies control which type of storage is provided for the virtual machine and how the virtual machine is placed within the storage. They also determine data services that the virtual machine can use.
- You use the VM Storage Policies interface to create a storage policy.
- When you define the policy, you specify various storage requirements for applications that run on virtual machines.
- You can also use storage policies to request specific data services, such as caching or replication, for virtual disks.
- You apply the storage policy when you create, clone, or migrate the virtual machine.
- After you apply the storage policy, the SPBM mechanism assists you with placing the virtual machine in a matching datastore.
2.1 Storage Policies and Virtual Machines
After you define a VM storage policy, you can apply it to a virtual machine.
- You apply the storage policy when provisioning the virtual machine or configuring its virtual disks. Depending on its type and configuration, the policy might serve different purposes.
- The policy can select the most appropriate datastore for the virtual machine and enforce the required level of service.
- Or it can enable specific data services for the virtual machine and its disks.
If you do not specify the storage policy, the system uses a default storage policy that is associated with the datastore.
2.2 Default Storage Policies
When you provision a virtual machine on a datastore, you must assign to the virtual machine a compatible VM storage policy. If you do not configure and explicitly assign the storage policy to the virtual machine, the system uses a default storage policy.
VMware-Provided Default Storage Policy
The generic default storage policy that ESXi provides applies to all datastores and does not include rules specific to any storage type.
- ESXi offers the default storage policies for object-based datastores, vSAN or vVols. These policies guarantee the optimum placement for the virtual machine objects within the object-based storage.
- VMFS and NFS datastores do not have specific default policies and can use the generic default policy or a custom policy you define for them.
User-Defined Default Storage Policies
You can create a VM storage policy that is compatible with vSAN or vVols and then designate this policy as the default for vSAN and vVols datastores.
- The user-defined default policy replaces the default storage policy that VMware provides.
- Each vSAN and vVols datastore can have only one default policy at a time.
- You can create a single storage policy with multiple placement rule sets so that it matches multiple vSAN and vVols datastores. You can designate this policy as the default policy for all datastores.
- When the VM storage policy becomes the default policy for a datastore, you cannot delete the policy unless you disassociate it from the datastore
2.3 Virtual Disk Provisioning Policies
When you perform certain virtual machine management operations, you can specify a provisioning policy for the virtual disk file.
- The operations include creating a virtual disk, cloning a virtual machine to a template, or migrating a virtual machine.
- NFS datastores with Hardware Acceleration and VMFS datastores support the following disk provisioning policies.
- On NFS datastores that do not support Hardware Acceleration, only the thin format is available.
- You can use Storage vMotion or cross-host Storage vMotion to transform virtual disks from one format to another.
Thick Provision Lazy Zeroed
Creates a virtual disk in a default thick format.
- Space required for the virtual disk is allocated when the disk is created.
- Data remaining on the physical device is not erased during creation but is zeroed out on-demand later; on the first write from the virtual machine.
- Virtual machines do not read stale data from the physical device.
Thick Provision Eager Zeroed
A type of thick virtual disk that supports clustering features such as Fault Tolerance.
- Space required for the virtual disk is allocated at creation time.
- In contrast to the thick provision lazy zeroed format, the data remaining on the physical device is zeroed out when the virtual disk is created.
- It might take longer to create virtual disks in this format than to create other types of disks.
- Increasing the size of an Eager Zeroed Thick virtual disk causes a significant stun time for the virtual machine.
Thin Provision
Use this format to save storage space.
- For the thin disk, you provision as much datastore space as the disk would require based on the value that you enter for the virtual disk size.
- The thin disk starts small and at first; it uses only as much datastore space as the disk needs for its initial operations.
- If the thin disk needs more space later, it can grow to its maximum capacity and occupy the entire datastore space provisioned to it.
3. vSAN Storage Policy
vSAN requires that the virtual machines deployed on the vSAN datastores are assigned at least one storage policy. When provisioning a virtual machine, if you do not explicitly assign a storage policy to the virtual machine the vSAN Default Storage Policy is assigned to the virtual machine.
The default policy contains vSAN rule sets and a set of basic storage capabilities, typically used for the placement of virtual machines deployed on vSAN datastores.
3.1 vSAN Default Storage Policy
vSAN requires that the virtual machines deployed on the vSAN datastores are assigned at least one storage policy. When provisioning a virtual machine, if you do not explicitly assign a storage policy to the virtual machine the vSAN Default Storage Policy is assigned to the virtual machine.
The default policy contains vSAN rule sets and a set of basic storage capabilities, typically used for the placement of virtual machines deployed on vSAN datastores.
Specifications
Characteristics
The following characteristics apply to the vSAN Default Storage Policy.
- The vSAN default storage policy is assigned to all virtual machine objects if you do not assign any other vSAN policy when you provision a virtual machine.
- The VM Storage Policy text box is set to Datastore default on the Select Storage page.
- The vSAN default policy only applies to vSAN datastores.
- You cannot apply the default storage policy to non-vSAN datastores, such as NFS or a VMFS datastore.
- Because the default virtual machine storage policy is compatible with any vSAN datastore in the vCenter Server, you can move your virtual machine objects provisioned with the default policy to any vSAN datastore in the vCenter Server.
- You can clone the default policy and use it as a template to create a user-defined storage policy.
- You can edit the default policy if you have the StorageProfile.View privilege. You must have at least one vSAN enabled cluster that contains at least one host.
- Typically you do not edit the settings of the default storage policy.
- You cannot edit the name and description of the default policy or the vSAN storage provider specification. All other parameters including the policy rules are editable.
- You cannot delete the default policy.
- The default storage policy is assigned when the policy that you assign during virtual machine provisioning does not include rules specific to vSAN.
Resources
vSphere Virtual Machine Administration
Conclusion
The topic reviewed in this article is part of the VMware vSphere 7.x Exam (2V0-21.20), which leads to the VMware Certified Professional – Data Center Virtualization 2021 certification.
Section 1 - Architectures and Technologies.
Objective 1.3.3 – Describe storage policies
See the full exam preparation guide and all exam sections from VMware.
