Re: bdar: efficiently backup allocated bytes in file systems

[David Chinner <dgc@sgi.com>]

On Mon, Mar 17, 2008 at 06:13:27PM -0700, Zach Brown wrote:
> So, I had a fun time throwing together a utility last weekend.  I
> thought I'd share it sooner rather than later.
> 
> I found myself wanting to backup a copy of an ancient ~75g ext3 file
> system.  I got frustrated by of our utilities which don't saturate
> storage.  I wanted dd line rates but I also only wanted to copy
> referenced data.
> 
> So I threw something together which does that.  I made it work roughly
> like tar so that people have some idea what to expect.  So you can do
> something like:
> 
>  $ bdar -cf - /dev/sda3 | gzip -c > /tmp/sda3-backup.bdar.gz
> ...
>  $ zcat /tmp/sda3-backup.bdar.gz | bdar -xf - /dev/sda3
> 
> and it will do exactly what you would guess it would do after reading
> those command lines.
> 
> The bdar file format is just a header and then a series of regions of
> bytes described by their length and offset.  To create a bdar file from
> a file system bdar needs to know enough to figure out what extents are
> referenced.  Restoring a bdar is generic, though, it just stamps bytes
> into the target file.

Neat, Zach. You should look at xfs_copy - it does pretty much this for XFS
filesystems....

Cheers,

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