VMware Changed Block Tracking (CBT) and NFS uh oh!

Saw some twitter activity on this tonight and I knowing we work with many NetApp customers on VMware vSphere I figure this has probably already come up or will soon.

First, what is Change Block Tracking?  http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1020128

In a nutshell CBT is vSphere’s ability to track at a block level changes to virtual machines virtual hard disks.  Applications that use the vStorage API can then access this information to do a backup of the changed blocks on a virtual machine.

So, if you’re using NFS storage, such as NFS from a NetApp storage array you will want to turn off this feature if you are experiencing this issue documented here.  http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1031106


3 thoughts on “VMware Changed Block Tracking (CBT) and NFS uh oh!

  1. Dan,

    Thanks for this post. I am not having lockup issues, however I am having CBT funtionality problems across NFS (from a NetApp filer). Basically, I am not able to do VM Differential Snapshots using the CBT option enabled. Have you ever seen this on a NetApp? I was told from my Backup provider (Unitrends) that the VMWare API does not support CBT across NFS.

    Any thoughts? I have been trying to run this to ground for almost 6 months and yours was the first intellegent post that I found that discussed both CBT and NFS…..

  2. I have not heard anything more about this since I posted this original article, curious if you have applied the patch?

    VMware absolutely supports CBT on NFS http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1020128

    It is called out again as supported in the Virtual Disk API Programming Guide http://pubs.vmware.com/vsphere-50/topic/com.vmware.ICbase/PDF/vddk_prog_guide.pdf

    Note there are some differences in what is supported between NFS and VMFS.

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