Homedir backup (was Re: "Stateless Linux" project)

Stuart Ellis s.ellis at fastmail.co.uk
Wed Sep 15 23:48:17 UTC 2004


On Wed, 2004-09-15 at 19:57, Eli Carter wrote:
> 
> I think the way this should work is:
> 
> Can I make a _secure_ connection to _my_ server?
> (Think ssh connection with the keys set up to know that the other side 
> is who you think it is.)
> If so, start the backup process over that link.
> Do scheduling of the network traffic so user-initiated traffic gets 
> higher priority than the backup.  Keep in mind that the backup may be 
> initiated by the user as well and would need to get scheduled as such.
> The user needs a way to tell the system "Don't do that right now" in 
> case they are on an expensive link, or know something else the computer 
> doesn't know, can't know, or misunderstands.
> There should also be a user-configurable daemon (or whatever) that can 
> tell the backup system whether it should do its thing right now or not, 
> based on arbitrary factors.  For instance: battery life, disk is spun 
> down, we're  plugged into power, it's been X hours, we have Y kB of 
> deltas that need to be backed up, certain important files have been 
> modified, etc., etc.
> 
> Otherwise, you're confusing "where I am" with "what I can do". 
> Sometimes they correlate, but they aren't really the same.

I agree with this.  I'm not sure that it ought to matter where the
machine is, provided that the link is good.

Perhaps the most basic question for an automatic sync is "is the link
likely to disappear whilst I'm working ?"   We can guess that links with
certain qualities are bad (bandwidth too low, connection hasn't been
available or stable for a period of x seconds, user specifies that that
link should not be used for sync).

We can't automatically tell when the user will want to disconnect the
link themselves, so the concept of arranging completely automatic
(rather than scheduled) backups may be problematic unless the backups
can be safely broken up into small sets that can complete quickly.  The
Windows file sync software can automatically backup on login and
logout.  It drove me nuts that it would spend several minutes working
through my entire home directory after I had decided that I wanted to
switch off the laptop.






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