Discussions specific to the Microsoft Hyper-V hypervisor
haslund
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Cluster Change Block Tracking

Post by haslund » Mar 08, 2015 9:54 pm 1 person likes this post

Please correct me if I am wrong, but from what I have understood Veeams Hyper-V CBT saves CBT information locally on each individual node in a Hyper-V cluster.
This means if a host is offline for whatever reason, CBT will not be used for any VM in that cluster as soon as any host is offline.

Would you please consider saving CBT information together with the VM files, in a similar way as how ESXi handles it so that even if a host is offline (maybe being service or hardware fault), CBT can still be used for backups.

Thank you in advance.
Rasmus Haslund
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Vitaliy S.
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Re: Cluster Change Block Tracking

Post by Vitaliy S. » Mar 09, 2015 10:38 am

Hi Rasmus,

You're correct that CBT data is stored on the host, since CBT driver is installed on the hosts directly after you add them to the Veeam B&R console and is activated on the first job run against them.

Thanks for your feedback!

Gostev
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Re: Cluster Change Block Tracking

Post by Gostev » Mar 09, 2015 11:06 pm

rhaslund wrote:Would you please consider saving CBT information together with the VM files, in a similar way as how ESXi handles it so that even if a host is offline (maybe being service or hardware fault), CBT can still be used for backups.
In fact, this was our original implementation (when we released "v1" of our Hyper-V support). Something did not work well with storing CBT files on CSV though (don't remember what exactly, but major issues) - so we have re-architected this in the following release, resulting in the current implementation.

jmeisel
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Re: Cluster Change Block Tracking

Post by jmeisel » Mar 12, 2015 1:24 pm

Are you telling me that it's working now, Vitaly???
We are using CBT and we can see that the backed-up virtual machine is read completely. But only a few MB / GB were written to the repository.

Maybe I missunderstand something, but shouldn't CBT prevent that the whole source is read?

We are running a Windows 2012 R2 Cluster with 8 hosts and one huge CSV

foggy
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Re: Cluster Change Block Tracking

Post by foggy » Mar 12, 2015 1:36 pm

CBT should work fine, you'd better contact technical support directly and investigate why it is not used.

Vitaliy S.
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Re: Cluster Change Block Tracking

Post by Vitaliy S. » Mar 12, 2015 1:38 pm

If you're using CBT, then entire VM image should not be read. Do you see any warning messages in the job session?

bobdigby
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[Merged] Failed to create Change Tracking Time Stamp

Post by bobdigby » Mar 26, 2015 9:52 am

We use Veeam to backup our Hyper-V VM's on four nodes in a cluster on Server 2012 Datacenter.

We have had no problems with backing up or changing tracking messages recently.

Last night I turned one of our nodes within our cluster off to do some diagnostics outside of windows. When Veeam went to backup any VM on the cluster it came up with the following message:

"Failed to create change tracking time stamp for virtual disk file C:\ClusterStorage\Volume1\VMname\etc.vhdx"

It then reread the whole VM taking hours instead of minutes to backup each VM.

As soon as I turned the node back on (not actually hosting any VM's) the next backup worked fine without that message.

Does anyone know why this happened? I found this KB http://www.veeam.com/kb1934 which mentions if a node is offline it may cause problems but surely if the files are kept on the cluster and not the node why does every node have to be online for Veeam to work properly?

Cheers

Bob

Shestakov
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Re: Cluster Change Block Tracking

Post by Shestakov » Mar 26, 2015 11:19 am

Hello Bob, since CBT for cluster is node-based, when the host was powered off CBT was not used, that`s why it took longer to produce the backup.
So, the behavior is expected. Please review the thread for more info and ask additional questions if you have any. Thanks!

bobdigby
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Re: Cluster Change Block Tracking

Post by bobdigby » Mar 26, 2015 11:43 am

Hi Shestakov, why is this the case do you know?

Surely if you use a cluster the CBT should be stored on the cluster. The whole point of a cluster is to have redundancy and some people even power down nodes during the evenings when things are quiet in a large environment to save power. Having to have every node operational in the cluster for CBT to work seems like a bad design?

Thanks

Bob

Vitaliy S.
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Re: Cluster Change Block Tracking

Post by Vitaliy S. » Mar 26, 2015 11:55 am

Hi Bob, see Anton's response above for this decision made:
Gostev wrote:Something did not work well with storing CBT files on CSV though (don't remember what exactly, but major issues) - so we have re-architected this in the following release, resulting in the current implementation.
Thanks!

bobdigby
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Re: Cluster Change Block Tracking

Post by bobdigby » Mar 26, 2015 11:59 am

Ok fair enough I see this as a major down point though will this be re looked into at any stage do you know?

bobdigby
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Re: Cluster Change Block Tracking

Post by bobdigby » Mar 26, 2015 12:12 pm

In fact re reading Gostev comment I quote "so we have re-architected this in the following release, resulting in the current implementation." does this mean CBT should work now if a host in a cluster is offline or not? Can you confirm

Thanks

foggy
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Re: Cluster Change Block Tracking

Post by foggy » Mar 26, 2015 12:16 pm

No, this means that initially it was designed to work so, but then was re-architected to keep CBT data on each host, as you have observed it.

bobdigby
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Re: Cluster Change Block Tracking

Post by bobdigby » Mar 26, 2015 12:39 pm

Ok fair enough I see this as a major down point though will this be re looked into at any stage do you know?

Vitaliy S.
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Re: Cluster Change Block Tracking

Post by Vitaliy S. » Mar 26, 2015 12:44 pm

Not in the short term future, however if read some bloggers, for example mentioned in this thread, you can see that alternative ways of addressing this behavior might arise.

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