On 3/22/2011 12:24 PM, Tyler J. Wagner wrote:
> On Tue, 2011-03-22 at 13:09 -0400, Jeffrey J. Kosowsky wrote:
>> I think it would still be helpful to have a hook that would allow some
>> type of query of bandwidth available. Perhaps most users would never
>> use the hook but having the option to call an external routine and
>> return a bandwidth availability metric would be nice...
>
> It's good to discuss features, but I don't think it is productive to
> discuss features that don't exist on the underlying platform, or are
> outside the scope of BackupPC.
>
> How do you get a bandwidth availability metric? Short of trying to push
> data back and forth, you can't.

Most people would enter a fixed number for what they want backuppc to 
consume.  Even if you can test it, you don't know if it will stay the 
same.  But much of the beauty of backuppc is that perl assignments don't 
really matter if they are numbers or the result returned from executing 
something so if you have a way to get a meaningful value you could do it 
(perhaps at the expense of not being able to edit it in the web interface).

> Once you have that, how do you limit it?  Again, this is dependent on an
> existing bandwidth control system like TC, or the individual backup
> tools supporting it (like rsync --bwlimit).

In general, you just don't start backups that will exceed it - or at 
least don't start more than one.  It could be a little smarter over 
rsync by looking at the bwlimit setting but I'd expect the practical 
fallout (and a big win) to be simply limiting runs to one at a time 
within the groups.

 > BackupPC is just a (very
> awesome) front-end to the backup tools that do the copying. Not all of
> those tools have an in-built bandwidth limit system.
>
> I'm just trying to limit suggestions to what the developer would
> actually listen to, or could reasonably implement.

Amanda is similarly a scheduling wrapper for standard tools, but it has 
concepts both for bandwidth limiting per network segment and 
pre-estimating the size of runs before scheduling (more important to 
amanda where it wants to fill a tape with a mix of fulls and incrementals).

-- 
   Les Mikesell
    lesmikesell AT gmail DOT com



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