Actifio worked around the VMware CBT bug in 2012

There has been a lot of discussion lately about a VMware Change Block Tracking (CBT) bug that causes backup software to miss out on modified parts of VMDK files.  This results in corrupted backups.

The Register has had two articles about it:

Oct 27:  ESXi is telling fibs to backup software • The Register

Nov 3: VMware: Yep, ESXi bug plays ‘finders keepers’ with data backups • The Register

The articles point to this VMware Knowledgebase link, and mentions that there is no fix available from VMware.  Ouch!

Well of course since Actifio uses VMware Change Block Tracking (CBT) to capture images of VMs, my first thought was sh…    ahh actually this is child friendly blog…   but you get the idea.   Were petabytes of client data at risk of being bad?

Fortunately the answer is a resounding no.  Actifio does not depend on this particular API because we saw the potential for a flaw like this a long time ago.  In fact we changed the way we use the VMware APIs in 2012 to ensure this API could not affect us

Actually we were that concerned about data integrity when using external APIs that we developed a feature we call Fingerprinting to ensure the integrity of our images. With every image that Actifio creates, Actifio uses a sampling technique to confirm that the image created in Actifio’s storage pools is the same as the source we were fetching data from.  This applies to both VMs and to images created by our Connector software.

So with this Actifio customers can be assured that all available virtual images are free of any corrupt data due to CBT, backup calls, or any other capture procedures.


About Anthony Vandewerdt

I am an IT Professional who lives and works in Melbourne Australia. This blog is totally my own work. It does not represent the views of any corporation. Constructive and useful comments are very very welcome.
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2 Responses to Actifio worked around the VMware CBT bug in 2012

  1. Hi Anthony, I have been working in data protection for over 15 years and this to me does sound like a major concern. With this problem acknowledged by VMware that they no longer can with hand on their heart say that you can use CBT to successfully backup and restore data from the ESXi environment. The API appears to be flawed. As you state this does have serious implications for VMware users as this method cleverly replaces the need to have agents on every VM and all the administration this involves. This does raise a few questions for users such as
    Can my backup data be restored ?
    What is my business exposure ?
    and more importantly
    What are the legal implications for my organisation; for VMware ?
    I am sure VMware have got something in their small print of their agreements which will cover them answering the last question. But major storage manager products integrate with CBT as does Actifio, Fingerprinting that you mention is not widely known, I cannot find much about it. Does this solution assure us that Actifio guarantees that data can be successfully restored even though a link in the backup chain is broken.

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