When performing a restore of a full virtual machine or attaching VM disks to an existing virtual machine, you can change the disk provisioning on the Restore Options for All Selected Items dialog. The following disk provisioning types are available:
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Original: (default) Use the same disk provisioning that the source virtual machine used at the time of backup.
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Thick Lazy Zero: Use thick lazy zero provisioning to allocate disk space for all disks. This method only writes to sectors of the disk that contain data.
When this option is used to restore a thick eager zero disk, empty extents are written. In the vSphere client, the resulting restored disk will still be displayed as a thick eager zero disk.
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Thick Eager Zero: Use thick eager zero provisioning to allocate disk space for all disks. This method writes zeros to any unused sectors of the disk.
If the original source disk was provisioned as thin or thick eager zero, a restore that specifies thick eager zero provisioning can skip any empty sectors of the disk, because the empty sectors are already written with zeros. In this case, restore logs may indicate that the disk provisioning method was thick lazy zero.
When restoring from a thick lazy zero disk using thick eager zero provisioning, zeros are written to all empty sectors.
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Thin: Use thin provisioning to allocate disk space for all disks in the virtual machine.
When you restore a virtual machine that has thin disks on a NFS datastore, empty blocks on the disk are not restored; only the actual data on the disk is restored.
If Changed Block Tracking (CBT) was not functioning properly at the time of backup, the backed up disk data might be corrupt. To resolve this issue, reset CBT as described in Resetting Changed Block Tracking for VMware vSphere virtual machines (2139574), and then perform a new backup operation.