VMware passes Hyper-V up in the backup race

The title may surprise none of you, but it is actually the opposite of what I said 1.5 years ago in a blog post called Hyper-V ahead of VMware in the backup race

Back then I was concerned that VMware did not have full VSS support.  They have since rectified that. [Update: by “full VSS support,” what I mean is that it can talk properly to all versions of VSS.  Before, they did not support Windows 2008.  Now they support all versions of Windows.  There is still the problem that they only have one style of snapshot, so they aren’t telling applications that they’ve been backed up, which means that the applications aren’t truncating their logs.]

They also added changed block tracking (AKA “CBT”) in vSphere, so it is possible to perform block-level incrementals on image-level backups. And since VMware is talking properly to VSS, the applications are doing what they are supposed to be doing before a backup as well. 

Now it is Hyper-V that is behind.  There is no API within Hyper-V that can present to you a map of changed blocks in order to back them up.  You can perform an incremental backup of-course, but an incremental backup via the Hyper-V host is going to back up everything, as every .VDK file will have changed.

This changed blocked block tracking feature of VMware makes finding which blocks have changed must faster, and backing up just the blocks that have changed (vs the files that have changed) is the fastest way to do an incremental backup.

Just like with VMware, third parties have stepped in to fill the void.  So far, I know of Veeam and Arkeia that are using their source deduplication capabilites to perform sub-file incremental backup of Hyper-V machines.  I’m sure there are more as well — and if any of them mention themselves in a comment, I’ll update my post.

----- Signature and Disclaimer -----

Written by W. Curtis Preston (@wcpreston). For those of you unfamiliar with my work, I've specialized in backup & recovery since 1993. I've written the O'Reilly books on backup and have worked with a number of native and commercial tools. I am now Chief Technical Evangelist at Druva, the leading provider of cloud-based data protection and data management tools for endpoints, infrastructure, and cloud applications. These posts reflect my own opinion and are not necessarily the opinion of my employer.

11 thoughts on “VMware passes Hyper-V up in the backup race

  1. Rob Emsley says:

    Hi Curtis,

    You sure VMware has full VSS support? Even with VSphere 5.0 I thought they were only supporting Full Copy vs Full Backup.


  2. cpjlboss says:


    What I mean by full VSS support is that they can perform application level snapshots via VSS. They couldn’t do that before but Hyper-V could.

    You’re right that they could still do better. But at least we’re getting app-consistent snapshots.

  3. malexand says:

    Does this mean that VMware is not telling applications that they have been backed up, and therefore logs don’t get truncated etc? Does the backup application have to make an explicit call to do application-level snapshots?


  4. mitch808 says:

    Even today, to do ANY backup of databases that require VSS to properly be backed up, you must install an agent. Symantec, Veeam, Networker, Commvault, and possibly more. VMware tools (in ESX 3.x or 4.x) cannot simply do it alone without the help of a backup agent with proper VSS support. BackupExec does it cleaner than most doing image level, and it can trigger the agent on demand to do its thing. All others you do separate guest-level policies for Db’s, vs image level backups.

    CBT was also introduced in vSphere4, which has been out more than a year now, with vSphere5 now within sight… What did I miss on CBT, that isn’t already here today?

    Also a side note, ask each vendor how they do CBT restores… It varies greatly, with only one restoring the changed blocks, and all others restore the entire VMDK, but use CBT on backup operations.

  5. cpjlboss says:




    I’m not sure why you say what you’re saying. As long as the database has a VSS writer, there’s no reason that you can’t back it up via VSS and no agent. The only thing you don’t get is what Rob and Mark pointed out. You’re still properly backing them up. You’re just not truncating the logs.

  6. mitch808 says:

    Agreed! Though as pointed out, an agent can do log truncation too. It’s a constant battle I face in most places.. DBA’s doing SQL/Oracle dumps, managing the entire data protection scheme and maintenance, and Backup Admins trying to maintain retention policies per business requirements with auditable results.

    An agent can do the VSS backup, truncate the logs as needed, apply a specific retention, and report on the data/actions performed.

    I don’t disagree with what you said at all, it’s just whats the most business appropriate method, is usually agent based solutions.
    Of course we could just use circular logging, and problem solved! 😛

    [quote name=W. Curtis Preston]


    I’m not sure why you say what you’re saying. As long as the database has a VSS writer, there’s no reason that you can’t back it up via VSS and no agent. The only thing you don’t get is what Rob and Mark pointed out. You’re still properly backing them up. You’re just not truncating the logs.[/quote]

  7. Jerome Boutaud says:

    Hello Curtis,

    As always, I thoroughly enjoyed reading your post 🙂
    I just wanted to add to the information that Acronis Backup and Recovery 11 has the ability to create incremental level backups at the block level of Hyper-V without an agent inside the guest. In fact Acronis introduced this technology in Acronis Backup and Recovery 10. Acronis does this by identifying which block have changed on the virtual disk thus sending only the new blocks of used space to the destination regardless of deduplication options


  8. Migueld says:

    Hi Curtis,
    Avamar is doing VMware backups perfectly using all CBT features and even introcing one for some time now which is CBR “Change Block Restore” avoiding full restores but doing a kind of rool back on a previous state sending the only blocks needed to go back to a previous state. Also you can trigger the specific agent for free and doing so restore selective on apps like objects on Sharepoint, Exchange, etc…

  9. ohplease says:

    Gimme a break.
    The VM Ware Backup is for many Szenarios unuseable.

    A Rollback gives you only the state from a guest shutdown unclean.
    If you got Database/Ldap Aplications you can drop it.

    The Aplicationlevel Backup … uhm not really .. exchange backup? not really.

    All you got is a fullexchange backup but in 9)% the cases you need a Mailboxlevel backup – count for all Colab Mailsystems

    Same for all Database related backups – it doenst count you got the hole server if you can restore only a single database the backup is useless

    shure its easier but still a real aplication/filebased backup / hotbackup solution on each guest IS NESSSESARY

    Everything else isnt professional and not a solution.

    However as an additinal disaster recovery option its ok – IN ADDITION not as replacement

  10. cpjlboss says:


    Just because an Exchange backup was taken of a VM via an image and VSS doesn’t mean you can’t do mailbox recovery from it. That’s up to what the backup s/w company does with it. In fact, I know one large backup s/w company that ONLY does backups of Exchange/SQL/etc this way. In summary, just because you backed up the whole VM doesn’t mean that’s your only recovery option.

    Not sure what you mean in the rollback statement.

  11. malexand says:

    Symantec provide their own VSS provider with NetBackup 7.1 to replace the one in VMware Tools. This truncates the logs for Exchange backups only (not SQL Server or Oracle).

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