Re: bdar: efficiently backup allocated bytes in file systems

[David Chinner <dgc@sgi.com>]

On Tue, Mar 18, 2008 at 03:06:27PM -0700, Zach Brown wrote:
> 
> > Neat, Zach. You should look at xfs_copy - it does pretty much this for XFS
> > filesystems....
> 
> haha, yet another round of the -fsdevel XFS drinking game :)

/me grins

> Does xfs_copy tend to assert the XFS file format in the backup files it
> generates?

Yes. If the destination is a file, the resultant image is a sparse
file that is a mountable XFS filesystem.

> One of the things I was hoping for with bdar was to have the
> resulting copy image be agnostic.  It's just a sparse map with some
> checksumming, really.

Yup - the use of a sparse file avoids the need for an internal map.
But that does't really work for piping the output, though.
xfs_metadump is probably more similar to bdar in that respect, but it
doesn't copy data....

FWIW, xfs_copy is really for efficient duplication of one source
disk to many destination disks in manufacturing, not so much as
a filesystem backup tool...

> That limits what we can do, of course.  The current trivial format only
> has one address space which doesn't fit well with the plans file systems
> have of working with multiple addressable block ranges.

Can't do everything ;)

> But I think I'm fine with that.  The value:complexity ratio of this
> trivial version is refreshingly large.

Agreed. 

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group