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

On Thursday 16 September 2004 04:50 pm, Kyrre Ness Sjobak wrote:
> tor, 16.09.2004 kl. 02.09 skrev David Hollis:
> > On Thu, 2004-09-16 at 00:48 +0100, Stuart Ellis wrote:
> > > 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.
> >
> > Windows provides a good example of how it should not work.  It needs to
> > be something can be performed in the backgroun and can be interrupted
> > and recover gracefully.  And it shouldn't be triggered by login/logout.
> > Those are probably the times when the user wants it least.  In the
> > morning they boot up and want to get into email/web whatever to start
> > getting stuff done.  The last thing you need is the drive sitting there
> > chugging while it determines what it needs to sync.  At logout, you're
> > heading home the for the day, trying to beat traffic, etc and the last
> > thing you want is to have to wait for that 650MB iso you just downloaded
> > to sync!
> >
> >
> > --
> > David Hollis <dhollis davehollis com>
> Sounds kinda like the windows network at school - it has a 2-10 minutes
> login time - and a logout time which is something of the same. This is
> due to Windows dowloading the WHOLE profile - instead of the Unix model
> with hiden config file and the desktop as a folder. Makes quite a few
> use the Linux machines instead - they use 10 sec max - and that is when
> the server is under high load (it is one of the thick clients that was
> to old to run XP, no DMA support, while the windows guys got an Xeon
> with SCSI disks...), and using a slow machine (600 mhz celly/128 MB RAM
> running fc2).

Could we build a files-changed journal using dnotify or FAM, in order to get 
rid of the scanning time?

Ideally, you would know which parts of the file(s) were updated, and only ship 
those parts, but dnotify and FAM don't have that level of specificity,

If we took this approach, then we'd have a near-optimal update time.
The merge problem, of course, still exists, but it will -always- exist unless 
you update from the server on login and to the server on logout.


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