Need some help with my backup idea.

Jelle de Jong jelledejong at
Thu Sep 28 15:39:23 UTC 2006

Thanks for the information,

Dave Dodge wrote:
> I don't really have any answers, just comments:
> On Sun, Sep 24, 2006 at 04:32:18PM +0200, Jelle de Jong wrote:
>> Output must result in a one file image that can be mounted and read with 
>> the mount tool. (like a dd image)
> This requirement complicates things, because it means the kernel has
> to be able to read your backup format.  Using an existing filesystem
> format may not solve your problems because they're unlikely to have
> the space efficiency that you're after.  Your best solution here might
> be a custom format with a custom FUSE backend.
>> All file stored in the image must come out like they came in (not like 
>> some standard iso image)
> I'll complicate this further by adding some special cases that can be
> trouble:
>   - Large sparse files.  Many Unix-style filesystems will allow you to
>     create files that appear to be many times larger than all
>     available disk space.  I used to have 1.44M floppy disks with
>     30-40 gigabytes of files on each of them.  If you try to copy
>     these by opening and reading them you have to be careful to not
>     converting the missing blocks from the original into real blocks
>     in the copy; otherwise you end up using more disk space or even
>     running out entirely.
>   - Files with multiple hard links.  Ideally your backup and restore
>     procedure should preserve the links.
>   - If you back up on one machine and restore on another, what happens
>     when the UID and GID values don't match on the two machines?  Do
>     you need to record the user and group names rather than (or in
>     addition to) the UID/GID values?
>   - Extended attributes.  These become important in situations such as
>     using SELinux.
>> But this will not cover the split an join function.
> Unionfs might help with that.
>                                                   -Dave Dodge

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