Virtual disk configuration for VMware virtual appliances and virtual disk provisioning types

Excerpted from the VMware vCenter Client documentation

about the provisioning type (About Virtual Disk provisioning policies)

When you perform certain virtual machine management operations, such as creating a virtual disk, cloning a virtual machine to a template, or migrating a virtual machine, you can specify a provisioning policy for the virtual disk files.

The following disk provisioning policies are supported for NFS data storage and VMFS data storage with hardware acceleration capabilities. On NFS data stores that do not support hardware acceleration, only the compact format is available.

You can use Storage vMotion to convert a virtual disk from one format to another format.

Thick Provisioning Delay 0: Creates a virtual disk in the default thick format. Allocate the required space for the virtual disk during the creation process. Any data that is persisted on the physical device is not erased on creation, but it is zeroed as needed when the first write operation is performed from the virtual machine.

Thick provisioning 0: Create thick disks that support clustering features, such as Fault tolerance. Allocate the required space for the virtual disk when it is created. In contrast to the flat format, the data retained on the physical device is zeroed during the creation process. It may take longer to create a disk of this format than to create another type of disk.

Thin provisioning: Use thin provisioning format. Initially, a thinly provisioned disk uses only the data storage space that the disk originally needed. If you later need more space for a thin disk, it can grow to the maximum capacity allocated for it.

Attention:

1. If the virtual disk supports a clustered solution (such as Fault tolerance), do not set the disk to compact format.
2. If you need more space after a thin disk, it can grow to its maximum capacity and occupy the entire data storage space that is provisioned for it. Also, you can manually convert a thin disk to a thick disk.
3. According to personal judgment, the use of thick-provisioned 0 is more appropriate, and the most error-prone.

Virtual Disk Configuration

The appearance of the virtual hard disk page changes depending on the support and features of the virtual hard disk device.

Most of the information displayed (for example, the virtual disk file path for virtual disk file alternatives) is read-only, because the virtual hard disk device can be changed only if it is removed and re-added.

Even if the virtual machine is running, you can add the disk and add more space to the existing disk.

If the disk is backed up by a normal vdisk file:

• The disk mode control can be used to make advanced configuration of disk behavior, depending on the actual type of host.
• The SCSI node control can be used to make changes to the virtual device assignment on the virtual SCSI bus location.
• If the disk is backed up by a data store mapped physical storage device (RDM, for bare metal mapping):
• The location of the mapping file and the actual bare metal lun is displayed, which can be used to select the LUN path (alias) required to use the SAN.
• The compatibility mode for RDM is displayed. If the compatibility mode is virtual, the disk mode control is also displayed.
• The SCSI node control is provided in the same way as a normal virtual disk.

Change disk mode to exclude virtual disks from a snapshot

With snapshots, disk mode Describes how virtual hard disks can participate in snapshots.

Typically, a disk is just like working in a physical machine, with a snapshot mechanism that controls how changes are written to the disk. For some purposes, you can separate the disk from the snapshot mechanism so that the snapshot operation does not affect the contents of the disk. A standalone disk can be durable or non-durable.

Stand-alone persistence: The behavior of a persistent mode disk is similar to the behavior of a regular disk on a physical machine. All data written to the persistent mode disk will be permanently written to disk.

Standalone non-persistent: changes to non-persistent mode disks are lost when power is turned off for virtual machines or when a virtual machine is reset. With non-persistent mode, you can restart the virtual machine each time you use the same virtual disk state. Changes to the disk are written to the redo log file and read from, and the redo log file is deleted when the virtual machine shuts down power or resets.

Select a virtual Disk type

A virtual disk consists of one or more files in the file system that are displayed to the guest operating system as a single hard disk. These disks can be ported between hosts. You can create virtual disks, use existing virtual disks, or create bare device mappings (RDM), which can access the SAN directly through RDM.

During the creation of a virtual machine, you can use the Create Virtual Machine Wizard to add a virtual disk. To add disks at a later time, select the Do not create disk option and use the Add Hardware Wizard in the Virtual Machine Properties dialog box to add disks.

Note: You cannot reassign a virtual disk to another type of controller.

adding RDM disks (Bare device mappings)

You can store virtual machine data directly on a SAN LUN instead of storing it in a virtual disk file. This feature is useful if the application running in the virtual machine must store the physical characteristics of the storage device. In addition, by mapping San LUNs, you can manage disk storage using existing SAN commands.

When a LUN is mapped to a VMFS volume, VCenter Server creates a bare device mapping (RDM) file that points to the bare LUN. Encapsulating disk information into a file allows VCenter Server to lock LUNs so that only one virtual machine can be written to the LUN at a time. For more information about RDM, see vsphere Storage documentation.

RDM files have a. vmdk extension, but the file contains only disk information, which describes the mappings to the LUNs on the ESXi host. The actual data is stored on the LUN.

You can create an RDM as the initial disk for a new virtual machine, or add it to an existing virtual machine. When you create an RDM, you can specify which LUNs to map and which data store to use to place the RDM.

Note: You cannot deploy a virtual machine from a template and store its data on a LUN. Only its data can be stored in a virtual disk file.

Required Privileges:

1. Host. Local operations. Creating a virtual machine
2. Virtual machines-Checklist. Creating
3. Virtual machines-Checklist. Adding a new disk

Steps

1. On the Select Disk page, select [Bare Device mapping], and then click Next.
2. From the list of SAN disks or LUNs, select the LUNs that the virtual machine can access directly, and then click Next.
3. Select the data store for the LUN mapping file, and then click Next.
4. You can place RDM files on the same datastore where the virtual machine configuration files reside, or you can choose a different data store.

Note: To use VMotion with NPIV-enabled virtual machines, make sure that the RDM files for that virtual machine reside on the same datastore. Storage vMotion or vMotion cannot be performed between data stores after NPIV is enabled.

1. Select a compatibility mode, and then click Next.
2. Physical: Allows the client operating system to access the hardware directly. The physical compatibility mode is useful if you are using a SAN-aware application in a virtual machine. However, a virtual machine with a physically compatible RDM cannot be cloned, cannot be made into a template, or migrated (if the migration involves a replication disk).
3. Virtual: Allows RDM to work like a virtual disk, so you can use features such as snapshot and clone execution. When you clone a disk or make it into a template, the contents of the LUN are copied to the. vmdk vdisk file. When migrating a virtual compatibility mode RDM, you can migrate the mapping file or copy the contents of the LUN to the virtual disk.
4. Click [Next].

End

Virtual disk configuration for VMware virtual appliances and virtual disk provisioning types