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user data sync (Re: "Stateless Linux" project)



On Tue, 2004-09-14 at 13:20 +0100, Stuart Ellis wrote:
> 
> The issue of backing up user home directories from mobile devices in
> mentioned in the PDF, but I'd be very interested in hearing about
> approaches for dealing with syncing shared data stores.
> 
> With a home directory or private data store basic sync works if it can
> be made transparent to the user, and/or integrated into the GUI
> (Off-line Files on MS Windows, Mac iDisk).
> 
> Writable shared data stores presumably require some form of
> reconciliation or version control for multiple off-line copies to be
> handled smoothly.  I suppose that one solution might be to wrap access
> to a version control system into the standard GUI so that the
> functionality becomes accessible to office workers; another might be to
> use a database-backed system like Storage, which could replicate.
> 
> How are people dealing with this issue on their networks now ?  What do
> we think would be the "Just Works" solution in the context of Stateless
> Linux ?

A sentiment around the office is that the "merge" concept is impossible
to sanely present to users, and so instead we should stick to "master
copy" and "backups"

Here is one UI idea which may be attributable to Bryan and Seth or may
be something they wish to disown.

In any case, imagine you have two laptops, "Thinkpad" and "Inspiron",
and a workstation "Optiplex". The Thinkpad is currently on the network,
and the Inspiron is disconnected. You might see the following on the
desktop of each system, in place of the current "hp's Home":

  Thinkpad Desktop:

       [icon]
      Thinkpad

       [icon]
      Copy of Inspiron

       [icon]
      Optiplex

  Inspiron Desktop:

       [icon]
      Inspiron

  Optiplex Desktop:

       [icon]
      Optiplex

       [icon]
      Thinkpad

       [icon]
      Copy of Inspiron

So the "Copy of Inspiron" is a read-only backup of your Inspiron homedir
(kept on some network share). The other icons are the actual homedirs on
those systems. If you imagine I now connect the Inspiron, my Optiplex
desktop changes in real time:

       [icon]
      Optiplex

       [icon]
      Thinkpad

       [icon]
      Inspiron

And if I disconnect the Thinkpad, then instantly Optiplex displays:

       [icon]
      Optiplex

       [icon]
      Copy of Thinkpad

       [icon]
      Inspiron

In the above example, the disconnected Inspiron didn't have "Copy of
Optiplex" or "Copy of Thinkpad" but optionally you could have that, if
you were willing to use the disk space to keep a disconnected copy
rather than having "Copy of Foo" be a read-only network file share.

This example is pretty contrived; making up numbers, I bet
conservatively the 90% or more case is the user has only one computer,
and the 98% case is only two, and the 2% case is more than two.
We might also want to think about the user having a user-specific
laptop, and then using multiuser sort of desktop systems. In that case
perhaps there's a single network NFS homedir used for all desktop
systems, and then a homedir for each laptop.

Anyway, the basic point is there's only one writable copy of each
homedir (the copy that lives on the laptop itself), and multiple read-
only copies.

For a file share used by multiple users, a simple approach is that they
have a read only copy on their laptop, and it changes to the writable
actual share while they are connected. Or just vanishes while
disconnected, if appropriate.

Just having reliable homedir backup, plus the above UI, would be very
useful and dramatically better than what most people use today. Maybe a
complex merge solution would be even better, but those solutions never
seem to catch on even though they've been implemented many times...

Havoc




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