vSphere 6.0: Virtual Disk Types (Part-10)

In previous post of this series, we’ve discussed virtual hardware and virtual version of a VM. And in this post, we’ll discuss about virtual disk and its types for a VM. if you missed previous posts of this series, you can follow them here.

  1. Introduction to vSphere 6.0
  2. Introduction to Virtual Infrastructure
  3. vSphere 6.0 Lab Setup
  4. vSphere Client 6.0
  5. Install and Configure ESXi 6.0
  6. Configure IP Address and Hostname of ESXi 6.0
  7. Configure NTP Client using vSphere Web Client 
  8. Understanding Virtual Machine Files
  9. Virtual Machine Virtual Hardware

A virtual machine usually has at least one virtual disk. Adding the first virtual disk to a VM implicitly adds a virtual SCSI adapter to complete the connection. An ESXi host offers the following adapters.

  • Bus Logic Parallel
  • LSI Logic Parallel
  • LSI Logic SAS
  • VMware Paravirtual SCSI
  • AHCI SATA controllers

The typical configuration option of the VM creation Wizard in vSphere Client or Web Client selects the type of virtual SCSI adaptor, based on the selection of guest OS. By default, virtual disk is stored in the same folder as configuration file of a VM is stored. However, virtual disk can be stored on different location other than the configuration file stored for just separating the boot and data disks.

When a virtual disk is created for a VM, following disk types are available.

  1. Thin Provision, ii. Thick Provision
  2. Thin Provision: A thin-provisioned disk uses only as much datastore space as the disk initially needs. If the thin disk needs more space later, it can expand to the maximum capacity allocated to it.
  3. Thick Provision: Thick provisioning uses all the defined disk space at the creation of virtual disk. It further has following two types.
  • Thick Provision Lazy Zeroed: Space required for virtual disk is allocated during creation. Every block is filled with a zero when data is written on the block. This type is the default disk type.
  • Thick Provision Eager Zeroed: Space required for virtual disk is allocated during creation. Every block is prefilled with zeros.

Disk Provisioning

Configuration of Thin and Thick provisioning in storage virtualization will be discussed in details in future posts.

Thin Provision

                                 Figure: Thanks to VMware

In above figure, you can see that we have a datastore with thick and thin provisioned virtual disks. A full 20GB disk is allocated and occupied in first VM with the Thick provisioned virtual disk. In second VM, you can see that virtual disk type is Thin provisioned, 40GB is allocated and 20GB is occupied as its data size is 20GB. And in third VM, where virtual disk type is Thin provisioned, and it is as same as the 2nd VM where 80GB disk space is allocated and it occupied 40GB as its data size is 40GB.

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