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VSICM51 - Slide 08-10 - Changed Block Tracking



1. Wrong:

When describing the CBT file functionality, slide notes state:

The state of each file is located in this file.
1. Correct:

Actually the state of each block is stored in the CBT file.

1. Info:

For more details see the "vSphere Data Protection Administration" guide, "Understanding vSphere Data Protection" chapter, "Introduction to vSphere Data Protection" paragraph.

1. Source:

vSphere Data Protection 5.1 Administration Guide.



2. Room for improvement:

Slide notes mention that CBT can be used on any type of virtual disk and datastore. They also cite the physical compatibility mode RDM exception. Yet the list is not complete.
For a thorough description, consider the following:

  • Changed block tracking is supported whenever the I/O operations are processed by the ESXi storage stack:
    • For a virtual disk stored on VMFS, no matter what backs the VMFS volume (SAN or local disk).
    • For a virtual disk stored on NFS.
    • For an RDM in virtual compatibility mode.
  • When I/O operations are not processed by the ESXi storage stack, changed block tracking is not usable:
    • For an RDM in physical compatibility mode.
    • A disk that is accessed directly from inside a VM. For example if you are running an iSCSI initiator within the virtual machine to access an iSCSI LUN from inside the VM, vSphere cannot track it.
2. Source:

vSphere 5.1 Documentation Center - Gathering Changed Block Information paragraph.


Last modified onThursday, 12 December 2013 19:21
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