VMware "exclude data disks"

Ah! That message is fine - just a default warning when you change a Flashbackup-Windows Policy to a VMware one.

Perhaps that one has one disk but multiple volumes on it - or the boot partition is not on the C drive?

As per the manual: (so lots of possible issues)

The VMware - Advanced Attributes dialog has an option called Virtual disk
selection. The default setting is Include all disks. You should use this setting in
most cases.
The other options are Exclude boot disk and Exclude data disks. These options
are intended for the virtual machines that have multiple virtual disks. You should
use these options with care.
To exclude a boot disk or data disk, note the following requirements:
■ The virtual machine must have more than one disk.
■ NetBackup must be able to identify the boot disk.
■ The boot disk must not be part of a managed volume (Windows LDM or Linux
LVM). The boot disk must be fully contained on a single disk.
The boot disk must include the following:
■ The boot partition.
■ The system directory (Windows system directory or Linux boot directory).
■ The full swap file (Windows pagefile.sys or Linux swap partition).
Important! The exclude disk options are meant only for the following cases:
■ Excludebootdisk: Consider this option if you have another means of recreating
the boot disk, such as a virtual machine template for boot drives. If Exclude
boot disk is enabled, the policy does not back up the boot disk.
Note: When the virtual machine is restored from the backup, the virtual
machine data for the boot disk may be missing or incomplete.
Note the following about Exclude boot disk:
■ If the virtual machine has a boot disk but has no other disks, the boot disk
is backed up. It is not excluded.
■ If the virtual machine's boot disk is an independent disk, but the virtual
machine has no other disks, the boot drive is backed up. The restored boot
drive however contains no data, because NetBackup cannot back up the
data in an independent disk.
■ If the virtual machine has a boot drive and an independent drive, the boot
drive is not backed up. Only the independent drive is included in the backup.
Since NetBackup cannot back up the data in an independent disk, the
restored independent disk contains no data. Refer to the explanation on
independent disks in the following topic:
See “NetBackup for VMware terminology” on page 22.
■ Adding a virtual disk and changing this option before the next backup can
have unexpected results.
See “Virtual disk selection options: examples to avoid” on page 61.
■ Excludedatadisks: Consider this option if you have a different policy or other
backup program that backs up the data disks. If Exclude data disks is enabled
in a policy, that policy does not back up the data disks.
Note the following about Exclude data disks:
■ If the virtual machine has only one disk, such as C, the C drive is backed
up. It is not excluded.
■ If the virtual machine's boot disk is an independent disk, and the virtual
machine has a separate data disk, the boot disk is backed up. The restored
boot disk however contains no data, because NetBackup cannot back up
the data in an independent disk.
Caution: Use of the exclude disk options can have unintended consequences if
these rules are not followed.
The following topic contains important guidance on the exclude disk options:
See “Virtual disk selection options: examples to avoid” on page 61.
Virtual disk selection options: examples to avoid
You should use the Virtual disk selection option with care. For example, if you
add a disk to the virtual machine and change the Virtual disk selection setting,
note: The next backup may not capture the virtual machine in the state that you
intended. You should back up the entire virtual machine (Includealldisks) before
using Virtual disk selection to exclude a disk from future backups.
Note:Whenyou change an exclude disk option to disabled, do a full backup (Virtual
disk selection set to Include all disks) before the next incremental or differential
backup.