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Re: [rdiff-backup-users] Proposal to fix long filenames


From: Sheldon Hearn
Subject: Re: [rdiff-backup-users] Proposal to fix long filenames
Date: Sat, 12 Nov 2005 12:02:45 +0200
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On Saturday 12 November 2005 08:22, Ben Escoto wrote:
> So, any comments?  Anyone see any other drawbacks/problems?

I think this is another edge case that speaks to the value of entirely 
virtualizing the backup store.  In other words, don't rely AT ALL on 
the capabilities of the filesystem used to store backups, except for 
those capabilities common to all documented as being supported for 
rdiff-backup servers.  In real terms, this leaves you with pretty short 
names and just about nothing else.

Instead, use the backup store's filesystem only to store the data 
associated with backed up objects (files, directories and links), and 
use metadata to express all other attributes of those objects.

At the extreme, every object gets a serial number which is used as its 
name in the backup store's filesystem.  That serial number is used to 
index into the metadata store, to discover the properties of the object 
as it should be restored, including ownership, permissions, extended 
attributes, NTFS permissions, creation, modification and access times 
and checksums.

Directories can be virtualized in the same way.

This addresses more than just long filenames.  It also addresses my 
"Write-once read-many problem" issue, as well as the issue of 
rdiff-backup losing permissions when backing up from NTFS to UFS and 
then restoring back to NTFS.

It sidesteps an entire family of problems that arises out of what I 
consider to be a design limitation -- rdiff-backup does not seem to 
have been originally designed to be as cross-platform a utility as 
people would now like it to be.

This is one of the challenges that successful software inevitably 
faces. :-)

Ciao,
Sheldon.

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