[Box Backup] NTFS junction/reparse point

[Chris Wilson]

Hi Achim,

On Thu, 17 Nov 2011, Achim J. Latz wrote:
> On 24/10/2011 22:42, Chris Wilson wrote:
>
>> On recent Windows versions that have C:\Users, C:\Documents and Settings
>> is just a reparse point that points to that folder, for backwards
>> compatibility. C:\Users should be backed up normally, although some
>> folders in user home directories are also reparse points for the same
>> reason. Do you see it in your backups?
>
> I can see that the data is indeed backed within the "original" directory. I 
> am coming from an end-user perspective:
>
> 1) The user saved something important in "C:\Documents and 
> Settings\username\BIGDEAL.doc".

If they are a Windows Vista/7 user then they should not be saving anything 
in "C:\Documents and Settings". That directory is not visible to them. 
They should not know it's there. As far as they are and should be 
concerned, it's C:\Users. PEBCAK.

> Through NTFS junctions, the data is physically stored in 
> "c:\Users\username\BIGDEAL.doc", but the user does not know this, and 
> can easily open the file from within "Documents and Settings" for the 
> time being.

How? I can't see that folder on Windows 7.

>> If we backed up C:\Documents and Settings as well as C:\Users, I think 
>> you'd have two copies of the same data.
>
> I understand that, and I agree that uploading the same data again makes no 
> sense (unless there would be an amazing new deduplication feature, which 
> would eliminate all additional space requirements for the additional backups 
> of the same file, just like in Cumulus or BackupPC).

I'm afraid it's not going to happen in a hurry.

> Basic question: How could we "hang in" the corresponding data from the 
> NTFS junction points at all "links/mount points", so that the data is 
> only stored once, but the user sees it in all the places he is familiar 
> with?

This is quite a Windows-specific "feature" for Box Backup to have. I'd 
prefer not to add it if it's at all possible to avoid it.

If it's really essential, after considering the caveats above, perhaps we 
can either special-case (hard code) these directories in whatever client 
the user is using, or we can back up junction points (as Charles 
suggested) as a special object type that points back to the target of the 
junction point.

Under Windows, all of a user's data (the stuff that Box Backup is designed 
to back up) should be under c:\users anyway, so the only location you 
should need is this:

Location
{
 	Name = Documents and Settings
 	Path = c:\users
}

which solves the problem in a different way.

Cheers, Chris.
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