Metadata Handling

VMware provides a mechanism for virtual disk metadata, but it is seldom used.

Read Metadata Key from Disk

vixError = VixDiskLib_ReadMetadata(disk.Handle(), appGlobals.metaKey, &val[0], requiredLen, NULL);

Retrieves the value of a given key from disk metadata. The metadata for a hosted VMDK is not as extensive as for managed disk on an ESX/ESXi host. Held in a mapping file, VMFS metadata might also contain information such as disk label, LUN or partition layout, number of links, file attributes, locks, and so forth. Metadata also describes encapsulation of raw disk mapping (RDM) storage, if applicable.

Get Metadata Table from Disk

VixDiskLib_GetMetadataKeys() retrieves all existing keys from the metadata of a virtual disk, but not the key values. Use this in conjunction with VixDiskLib_ReadMetadata().

vixError = VixDiskLib_GetMetadataKeys(disk.Handle(), &buf[0], requiredLen, NULL);

Here is an example of a simple metadata table. Uuid is the universally unique identifier for the virtual disk.

adapterType = buslogic

geometry.sectors = 32

geometry.heads = 64

geometry.cylinders = 100

uuid = 60 00 C2 93 7b a0 3a 03-9f 22 56 c5 29 93 b7 27

Write Metadata Table to Disk

VixDiskLib_WriteMetadata() updates virtual disk metadata with the given key-value pair. If the key-value pair is new, it gets added. If the key already exists, its value is updated. A key can be zeroed but not deleted.

vixError = VixDiskLib_WriteMetadata(disk.Handle(), appGlobals.metaKey, appGlobals.metaVal);