vSphere Storage - ESXi 5.1 - Documentation - VMware
vSphere Storage - ESXi 5.1 - Documentation - VMware
vSphere Storage - ESXi 5.1 - Documentation - VMware
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<strong>Storage</strong> Thin Provisioning 22<br />
With <strong>ESXi</strong>, you can use two models of thin provisioning, array-level and virtual disk-level.<br />
Thin provisioning is a method that optimizes storage utilization by allocating storage space in a flexible ondemand<br />
manner. Thin provisioning contrasts with the traditional model, called thick provisioning. With thick<br />
provisioning, large amount of storage space is provided in advance in anticipation of future storage needs.<br />
However, the space might remain unused causing underutilization of storage capacity.<br />
The <strong>VMware</strong> thin provisioning features help you eliminate storage underutilization problems at the datastore<br />
and storage array level.<br />
This chapter includes the following topics:<br />
n “<strong>Storage</strong> Over-Subscription,” on page 225<br />
n “Virtual Disk Thin Provisioning,” on page 225<br />
n “Array Thin Provisioning and VMFS Datastores,” on page 230<br />
<strong>Storage</strong> Over-Subscription<br />
Thin provisioning allows you to report more virtual storage space than there is real physical capacity. This<br />
discrepancy can lead to storage over-subscription, also called over-provisioning.<br />
When you use thin provisioning, you should monitor actual storage usage to avoid conditions when you run<br />
out of physical storage space.<br />
Virtual Disk Thin Provisioning<br />
When you create a virtual machine, a certain amount of storage space on a datastore is provisioned to virtual<br />
disk files.<br />
By default, <strong>ESXi</strong> offers a traditional storage provisioning method for virtual machines. With this method, you<br />
first estimate how much storage the virtual machine will need for its entire life cycle. You then provision a<br />
fixed amount of storage space to its virtual disk in advance, for example, 40GB, and have the entire provisioned<br />
space committed to the virtual disk. A virtual disk that immediately occupies the entire provisioned space is<br />
a thick disk.<br />
<strong>ESXi</strong> supports thin provisioning for virtual disks. With the disk-level thin provisioning feature, you can create<br />
virtual disks in a thin format. For a thin virtual disk, <strong>ESXi</strong> provisions the entire space required for the disk’s<br />
current and future activities, for example 40GB. However, the thin disk uses only as much storage space as the<br />
disk needs for its initial operations. In this example, the thin-provisioned disk occupies only 20GB of storage.<br />
As the disk requires more space, it can grow into its entire 40GB provisioned space.<br />
<strong>VMware</strong>, Inc. 225