[BBLISA] Backing up sparse files ... VM's and TrueCrypt ... etc

[Dean Anderson]

Sure.  Incremental 'dump' sends the whole file, but upon sending it is
compressed. Being lots of zeros, the portion of the stream containing
the sparse file should still compress well.  

Also, assuming the tape is on a tape server, remember to do the
compression on the host rather than the tape server.  Something like:

  dump | gzip |(netconn) dd

Sending just the changed blocks is quite hard, as most filesystems don't
know what blocks have changed.  But ideally, the backup system doesn't
care how the file is represented in blocks, but merely sees streams
going on and off tape at its preferred blocksize.


		--Dean

On Sat, 20 Feb 2010, Edward Ned Harvey wrote:

> > > > Doesn't compression do very well on a long string of zeros?
> > >
> > > Yes, but how do you do the incremental?
> > 
> > dump | gzip | dd
> > 
> > (dd is necessary to get efficient blocksize on many tapes anyway.)
> > 
> > gnu tar also does incremental dumps, and might be suitable for windows.
> 
> Sorry, we were talking about doing incremental backups of sparse files,
> sending just the changed blocks, instead of sending the whole files again.
> Dump and tar can do incrementals of a filesystem or directory, based on
> things like timestamp and filesize to detect whether a file has changed, and
> then sending the whole file again.
> 
> 
> 

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