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TheOnlyWizard17
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ReFS Repository and Veeam

Post by TheOnlyWizard17 » 5 people like this post

Hi,

I've got a question about the use of a ReFS repository.
When you create a job to do backups, and specify to use "per VM backup files" on the repository, Veeam nicely creates a folder per job, and places the backup files, one per VM in there...
According to this paper from Microsoft however, https://docs.microsoft.com/en-us/window ... ted-parity
There's an important remark:
"We recommend placing write-heavy VHDs in different subdirectories. This is because ReFS writes metadata changes at the level of a directory and its files. So if you distribute write-heavy files across directories, metadata operations are smaller and run in parallel, reducing latency for apps."

So, following this logic, wouldn't it be better for Veeam to do per VM files also in per VM folders, so all metadata-operations like merges, transformations, fast clone operations etc. all can run in parallel instead of sequentially ?

PetrM
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Re: ReFS Repository and Veeam

Post by PetrM »

Hello,

Many thanks for the idea provided! I think it makes sense to analyze this approach a bit deeper in order to estimate potential performance gain and decide on this improvement depending on results of the research.

Thanks!

Steve-nIP
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Re: ReFS Repository and Veeam

Post by Steve-nIP »

Very interesting indeed. I really hope this gets tested thoroughly, and implemented quickly if it gives gains. ReFS on 2019 can use all the help it can get.

Gostev
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Re: ReFS Repository and Veeam

Post by Gostev »

I have just checked with the ReFS development team on this. While they confirmed the recommendation is correct, this approach will make difference only if the bottleneck is flushing dirty ReFS metadata, which I not currently known to be a bottleneck for the type of workload Veeam creates on ReFS, even in the largest of environments. Nevertheless, we will keep that in mind if we see this operation becoming an issue in certain scenarios. So, thanks for bringing this to our attention!

dimaslan
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Re: ReFS Repository and Veeam

Post by dimaslan »

Also,
That would only be an issue when the backup job contains multiple VMs.

Gostev
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Re: ReFS Repository and Veeam

Post by Gostev »

This is 99.99% of cases though ;) only the tiniest customers do one VM per job, and for them the bottleneck be their low-end hardware anyway.

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