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Multiple AVHDX disks point to the same parent - how to merge?

Anonymous
2024-11-21T05:12:36+00:00

Hello. I have a Server 2022 VM (on 2022). Aattched to the VM are additional differencing disks that are used to store shared files. My backup (Veeam) backs-up the differencing disks as a File Share, but it looks like about a month ago, it started having problems as there are a total of 9 avhdx files now. I'v inspected the disks and the chain goes like 1-2-3-4 (ie, lower number is a parent of the higher number). However, files 5-9 all point to #4 as a parent. It does not look like the VM has any problems booting (it's virtual disks are fine) so really, no errors. But the data in the disks are missing however.

So I'm thinking of manually merging them - if they were all in a single line, I understand that I go from newest to oldest (ie 4-3-2-1), but how do I merge disks 5-9? 9-4, 8-4, 7-4, 6-4, 5-4? or the other way? 5-4, 6-4, 7-4, 8-4, 9-4?

Thanks in advance for any info.

Windows Server High availability Virtualization and Hyper-V

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  1. Anonymous
    2024-11-22T13:54:47+00:00

    Hello

    Start with the most recent differencing disk and merge it with the parent. Since files 5-9 all point to 4, you should merge the highest differencing disk (9) into its parent (4) first. Follow this order: 9 to 4, 8 to 4, 7 to 4, 6 to 4, 5 to 4. I can reproduce multiple differencing disks pointing to the same parent disk in my environment.

    Image

    Note: Before doing any merges, make sure you have a backup of all differencing disks (AVHDX files) and the parent vhdx file. This step is critical to prevent any data loss.

    Best Regards

    Zunhui

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  1. Anonymous
    2024-11-25T21:38:44+00:00

    Thanks for this information. I'm not exactly sure if this works or not. I tried to do as your instructions, but was having problems merging the second disk (#8) after the first merge. I'm not sure if it was an issue with the process or there were issues with the sequence or assigned parents.

    I ended up merging each disk, starting with the newest, with the common parent, then comparing the contents to the unmerged version, and copying the difference. Restored the parent, merged it with the next newest, compared it with the original, copied the difference, etc.

    I was able to get the lost data this way, although this could get extremely tedious if you have a lot of disks and/or data.

    I still have the differencing disks and may try to attempt this again using your procedure.

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