[pbs-devel] PBS File Retore for NTFS with deduplication enabled leads to corrupted files

[Fabian Grünbichler]

On April 27, 2022 6:30 am, Dietmar Maurer wrote:
>> Think he would like to restore files from a windows Server (like a fileserver) with "Windows dedup" enabled on a volume.
>> Win Dedup works with chunk-files in "System Volume Information" Folder and metadatafiles to the "chunk-data".
>> 
>> We also use Win Dedup on File Servers
> 
> And you can reproduce the problem?
> 

see (German) https://forum.proxmox.com/threads/file-restore-dateien-defekt.108257

we could see whether ntfs-3g works better, but I am afraid from what I 
read in their issues they are playing a bit of cat and mouse with 
changes on the windows side, and the feature seems to not be backwards 
compatible in the windows world either, so chances are it will work 
better the older the VM's version of windows is.

alternatively, we could try to detect deduplicated files in the 
file-restore VM (based on some metadata?) and hard-fail the restore 
instead of returning valid-looking garbage.

users do report success with mapping + attaching the disk to an existing 
(version-matching) windows VM for manual file-restoring, so we could 
also think whether it's possible to streamline this approach somehow 
("attach disk RO from backup" on the PVE side?), since it's a lot more 
flexible for other use cases as well (e.g., encrypted disks inside the 
VM, storage management or FS we don't support in our file-restore VM, 
FS features that are not available in our file-restore VM kernel (yet or 
anymore ;)), ..). obviously an advanced use case, and for simple cases 
the existing file-restore approach is far nicer UX-wise.