Virtual Disk API Programming Guide - Documentation - VMware

To re-create data for any given day
1 Locate the -.vmdk redo log for the day in question.
is a sequence number. You can identify this redo log or snapshot by its timestamp.
2 Initialize the virtual disk library and open the redo log to obtain its parent handle.
3 Create a child disk with the VixDiskLib_Create() function, and attach it to the parent:
vixError = VixDiskLib_Attach(parent.Handle(), child.Handle());
4 Read and write the virtual disk of the attached child.
Practical Programming Tasks
This is just an example. On managed disk, multiple snapshots are not recommended for performance reasons.
Backup software on vSphere usually takes a snapshot, saves data to backup media, then deletes the snapshot.
Virtual Disk in Snapshots
The Virtual Disk API provides the following features to deal with the disk component of snapshots:
Attaching an arbitrary child in a disk chain
Opening read‐only virtual disks
Ability to open snapshot disk on ESX/ESXi hosts through VMware vCenter
Windows 2000 Read-Only File System
Another use of parent‐child disk chaining is to create read‐only access for Windows 2000, which has no option
for mounting a read‐only file system. In Figure 6‐1, the gray circle represents a virtual disk that must remain
read‐only because it has children. In this example, you want the Windows 2000 virtual machine to use that
virtual disk, rather than the newer ones C1 and C2. Create new child disk RO, attach to the gray virtual disk
as parent, and mount RO as the (mostly empty) read‐only virtual disk of the Windows 2000 guest OS.
Figure 6-1. Attaching Virtual Read/Write Disk for Windows 2000
RDM Disks and Virtual BIOS
This section outlines low‐level procedures for restoring raw device mapping (RDM) disks and NVRAM.
Restoring RDM Disks
C1 C2 RO
Backing up and restoring RDM disks presents unusual challenges. The original backed‐up RDM configuration
might not apply, and is probably not appropriate, if users restore:
A virtual machine to a different host or datastore.
Windows 2000
A virtual machine that was deleted, when its originally mapped RDM was also deleted, or the containing
LUN was repurposed and rewritten.
The RDM to a different virtual machine, even if that virtual machine is on the same host and datastore.
Users might do this to access files on the disk, or to test a restore.
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