Joshua Baker-LePain <jlb17 AT duke DOT edu> writes:

> On Thu, 29 Jul 2004 at 11:10am, Narada Hess wrote
> 
> > I was having estimation timeout failures, so based on advice from this
> > group (thanks), I increased the etimout value in amanda.conf from 600 to
> > 6000. Yay, now my backups work! But I am frankly astonished at the fact
> > that estimation took almost twice as long as the actual dump. Is this
> > normal, or is there some way to speed this up?
> 
> That depends.  The estimate phase with tar (which from below is what I 
> assume you're using) does tar cf /dev/null (among some other flags).  So 
> it just stats the files, it doesn't actually read them off the disk.  This 
> is generally *very* fast.  But if you have a case pathological to your 
> filesystem (e.g. *lots* of very small files), it can be slowed down 
> immensely.

I once watched top while I had the problem here. There is a phase in
GNU tar where it does no disc access but eats one CPU. Looks like it
is trying to sort the index of all files (probably sorting by inode in
order to find hardlinks).

So the case is not pathological to the filesystem but to GNU tar. cpio
avoids this; it simply writes the files out twice.

        Sven