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bathi
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Creating .avhdx in another folder?

Post by bathi » Feb 08, 2018 10:19 am

Hi,
It seems like an .avhdx file gets created eachtime a backup is taken.
So I got this VM with two hard drives, the first drive I guess is no problem, its on a das, but the second one is a physical SSD with only 185GB. It gets filled up pretty fast when the .avhdx file is created and then the VM get set on pause.
Is it possible to create those .avhdx somewhere else and not on the drive where .vhdx lies?
Its a SQL server so it gets pretty problematic if it stops :lol:

Mike Resseler
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Re: Creating .avhdx in another folder?

Post by Mike Resseler » Feb 08, 2018 12:54 pm 1 person likes this post

Hi bathi,

First: Welcome to the forums

The .avhdx is the differencing file that is created when you make a snap shot. You cannot change the location of that avhdx because it needs to be in the same location as the VHDX file.

Cheers
Mike

bathi
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Re: Creating .avhdx in another folder?

Post by bathi » Feb 08, 2018 1:33 pm

Hehe, thank you :)

Do you approximately know how much the .avhdx filesize is, if the .vhdx is set to 180GB?

It probably depends?

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Re: Creating .avhdx in another folder?

Post by Mike Resseler » Feb 08, 2018 1:45 pm

Yes it depends.

When you take a snapshot, the VHDX is made read-only and all writes are redirected to the created AVHDX. This is standard for Hyper-V, nothing we can do about it. After that the backup has been processed, we tell Hyper-V to go ahead and release the snapshot. At that moment the VHDX becomes read/write again and all of the differences that are recorded in the AVHDX are being merged into the VHDX (and then the AVHDX disappears). So depending on how long the backup takes, and how much data is being changed/ written during that time, the size can be small till very large.

Maybe a small idea, but seeing your concern is about a SQL server (and if it is an active one, that could mean a lot of changes quickly...) I would suggest to try to schedule the backup during a period where the SQL does not have much to do. Outside the business hours and outside the moments it does BI or maintenance jobs or similar

Hope it helps
Mike

bathi
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Re: Creating .avhdx in another folder?

Post by bathi » Feb 08, 2018 2:21 pm

Ok, I see.

Is it possible to turn off snapshots while taking backup, or does it have to stay at a read only state to be able to take backup of?

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Re: Creating .avhdx in another folder?

Post by Mike Resseler » Feb 08, 2018 2:30 pm

It is not possible. You need to have those snapshots or you might end up with data corruption

bathi
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Re: Creating .avhdx in another folder?

Post by bathi » Feb 08, 2018 2:35 pm

Ok, thanks again! :)

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Re: Creating .avhdx in another folder?

Post by Rumple » Feb 08, 2018 9:12 pm

it is totally possible...but not recommended...you can disable the hyperv integration which will do a crash consistent copy of the VM (aka, no snapshot) and then implement the application consistency so that it truncates logs and marks the databases as backed up.
SQL is actually pretty good at recovering itself most times from a crash (which is what it would look like), but if you have a 3rd party product doing real SQL backups then the risk is pretty minimal...schedule sql backups 30 minutes before the VMM snapshot and you have a pretty good recovery strategy without the risk from the snapshot files taking down the system...

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