VMware vSphere 7.x Study Guide for VMware Certified Professional – Data Center Virtualization certification. This article covers Section 1: Architectures and Technologies. Objective 1.3.1 – Describe storage datastore types for vSphere.
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 datastore types for vSphere
For objective 1.3.1 of the VMware vSphere 7.x exam, you need to describe storage datastore types for vSphere. Critical topics here are VMFS datastores, NFS datastores, vSAN datastores, and VMware vSphere Virtual Volumes (vVols).
To store virtual disks, ESXi uses datastores. Datastores are logical containers, analogous to file systems, that hide specifics of physical storage and provide a uniform model for storing virtual machine files. Datastores can also be used for storing ISO images, virtual machine templates, and floppy images.
Depending on the storage you use, datastores can be of different types.
vCenter Server and ESXi support the following types of datastores.
Depending on your storage type, some of the following tasks are available for the datastores.
1. VMFS Datastores
There is no doubt that this is the most important type of datatastore used by vSphere. This is a critical topic to master.
The datastores that you deploy on block storage devices use the native vSphere Virtual Machine File System (VMFS) format. It is a special high-performance file system format that is optimized for storing virtual machines.
- You need to use the vSphere Client to set up the VMFS datastore in advance on the block-based storage device that your ESXi host discovers.
- The VMFS datastore can be extended to span over several physical storage devices that include SAN LUNs and local storage.
- You can increase the capacity of the datastore while the virtual machines are running on the datastore.
- VMFS is designed for concurrent access from multiple physical machines and enforces the appropriate access controls on the virtual machine files.
1.1 VMFS Datastores Considerations
When you work with VMFS datastores, consider the following:
Versions of VMFS Datastores
Several versions of the VMFS file system have been released since its introduction. Currently, ESXi supports VMFS5 and VMFS6.
For all supported VMFS versions, ESXi offers complete read and write support. On the supported VMFS datastores, you can create and power on virtual machines.
For major characteristics of VMFS5 and VMFS6, see Versions of VMFS Datastores
VMFS Datastores as Repositories
ESXi can format SCSI-based storage devices as VMFS datastores. VMFS datastores primarily serve as repositories for virtual machines.
Sharing a VMFS Datastore Across Hosts
As a cluster file system, VMFS lets multiple ESXi hosts access the same VMFS datastore concurrently.
VMFS Metadata Updates
A VMFS datastore holds virtual machine files, directories, symbolic links, RDM descriptor files, and so on. The datastore also maintains a consistent view of all the mapping information for these objects. This mapping information is called metadata.
VMFS Locking Mechanisms
In a shared storage environment, when multiple hosts access the same VMFS datastore, specific locking mechanisms are used. These locking mechanisms prevent multiple hosts from concurrently writing to the metadata and ensure that no data corruption occurs.
Snapshot Formats on VMFS
When you take a snapshot, the state of the virtual disk is preserved, which prevents the guest operating system from writing to it. A delta or child disk is created. The delta represents the difference between the current state of the VM disk and the state that existed when you took the previous snapshot. On the VMFS datastore, the delta disk is a sparse disk.
2. Network File System (NFS) Datastores
An NFS client built into ESXi uses the Network File System (NFS) protocol over TCP/IP to access a designated NFS volume that is located on a NAS server. The ESXi host can mount the volume and use it for its storage needs. vSphere supports versions 3 and 4.1 of the NFS protocol.
- Typically, the NFS volume or directory is created by a storage administrator and is exported from the NFS server.
- You do not need to format the NFS volume with a local file system, such as VMFS.
- You mount the volume directly on the ESXi hosts and use it to store and boot virtual machines in the same way that you use the VMFS datastores.
- You can use NFS as a central repository for ISO images, virtual machine templates, and so on.
- You can connect the CD-ROM device of the virtual machine to an ISO file on the datastore.
- You then can install a guest operating system from the ISO file.
2.1 NFS Datastore Considerations
NFS Protocols and ESXi
ESXi supports NFS protocols version 3 and 4.1. To support both versions, ESXi uses two different NFS clients.
See more about NFS Protocols and ESXi
Firewall Configurations for NFS Storage
ESXi includes a firewall between the management interface and the network. The firewall is enabled by default. At installation time, the ESXi firewall is configured to block incoming and outgoing traffic, except traffic for the default services, such as NFS.
Using Layer 3 Routed Connections to Access NFS Storage
When you use Layer 3 (L3) routed connections to access NFS storage, consider certain requirements and restrictions.
Using Kerberos for NFS 4.1
With NFS version 4.1, ESXi supports the Kerberos authentication mechanism.
Set Up NFS Storage Environment
You must perform several configuration steps before you mount an NFS datastore in vSphere.
Configure ESXi Hosts for Kerberos Authentication
If you use NFS 4.1 with Kerberos, you must perform several tasks to set up your hosts for Kerberos authentication.
Collecting Statistical Information for NFS Storage
You can use the nfsStats tool in your ESXi host to display statistical information about NFS calls and Remote Procedure Calls (RPC). The command displays statistical information for NFS 3 and NFS 4.1 mounts on the ESXi host.
3. vSAN Datastore
After you enable vSAN, a single datastore is created. vSAN aggregates all local capacity devices available on the hosts into a single datastore shared by all hosts in the vSAN cluster.
vSAN datastore capacity
The size of the vSAN datastore depends on the number of capacity devices per ESXi host and the number of ESXi hosts in the cluster.
For example, if a host has seven 2 TB for capacity devices, and the cluster includes eight hosts, the approximate storage capacity is 7 x 2 TB x 8 = 112 TB. When using the all-flash configuration, flash devices are used for capacity. For hybrid configuration, magnetic disks are used for capacity.
Some capacity is allocated for metadata.
- On-disk format version 1.0 adds approximately 1 GB per capacity device.
- On-disk format version 2.0 adds capacity overhead, typically no more than 1-2 percent capacity per device.
- On-disk format version 3.0 and later adds capacity overhead, typically no more than 1-2 percent capacity per device. Deduplication and compression with software checksum enabled require additional overhead of approximately 6.2 percent capacity per device.
Upload Files or Folders to vSAN Datastores
You can upload vmdk files to a vSAN datastore. You can also upload folders to a vSAN datastore.
When you upload a vmdk file to a vSAN datastore, the following considerations apply:
- You can upload only stream-optimized vmdk files to a vSAN datastore..
- When you upload a vmdk file to a vSAN datastore, the vmdk file inherits the default policy of that datastore.
- You must upload a vmdk file to the VM home folder.
More about Upload Files or Folders to vSAN Datastores
4. VMware vSphere Virtual Volumes (vVols)
VMware vSphere Virtual Volumes (vVols) virtualizes SAN and NAS devices by abstracting physical hardware resources into logical pools of capacity. The vVols functionality changes the storage management paradigm from managing space inside datastores to managing abstract storage objects handled by storage arrays.
The VVols technology, along with vSphere 6, has been available since 2015 but the implementation of VVols has been slow. Probably slowed down due to the lack of storage vendor support. However, with the release of vSphere 7, further enhancements have been made to vSphere APIs for Storage Awareness (VASA) and VVols.
Historically, vSphere storage management used a datastore-centric approach. With this approach, storage administrators and vSphere administrators can discuss in advance the underlying storage requirements for virtual machines.
- The storage administrator sets up LUNs or NFS shares and presents them to ESXi hosts.
- The vSphere administrator creates datastores based on LUNs or NFS, and uses these datastores as virtual machine storage.
Typically, the datastore is the lowest granularity level at which data management occurs from a storage perspective. However, a single datastore contains multiple virtual machines, which might have different requirements. With the traditional approach, it is difficult to meet the requirements of an individual virtual machine.
More about vVols here: Working with VMware vSphere Virtual Volumes (vVols)
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 1.3.1 – Describe storage datastore types for vSphere.