Synchronizing xs-0.3 and xo-??? --- backups

[Martin Langhoff]

Hi Michael,

thanks for looking into this - I had the wikipage in my sight, but not
the bugs you listed. Excellent, reading up to fill the gaps.

>  Based on feedback from Peru, Mexico, and Nepal, the "restoration from
>  disaster-recovery backups" XO/XS coordination feature has been steadily
>  rising in priority. I also notice that "Backups" is your first line-item
>  on the XS-0.3 roadmap.

Yes. I was planning on looking at it next week, but happy to bump it up.

>  My large question is: "what changes need to be made to the XO's OS,
>  (currently to candidate-703) in order to make progress in this feature
>  cluster?"

I was hoping to say "here's a Python script that needs to be added to
the image and called opportunistically when NM tells us we are
connected to the XS (and at a regular interval during that situation)
and we have plenty battery or a powercord".

>  Sub-questions:
>
>   * What backup scheme do we actually intend to deploy? (Current choices appear
>    to be Wad's "dumb-rsync" method [1] and Ivan's method [2].

Wad's too simple, I am hoping to use a slightly simplified version of
Ivan's. For the restore part, I think I will drastically simplify
things from Ivan's approach.

>   * Does the chosen scheme permit us to sanely combine old backups with
>    an XO build that makes breaking changes to file layouts?

O-o-ouch! I imagine you are thinking about datastore overhaul insurance...? ;-)

Yes and no. My target layer is purely files, and we use rsync to copy
them over either way. *If* the datastore changes, and file layouts
change significantly, we'll copy that verbatim to the XS. If (for
restore purposes) the XO wants to read data from before the datastore
change, it will have to know how to... we'll just provide the old
files ;-)

... though the XS could provide translation services to help make that
easier. In practice, if the datastore stuff is today in a library on
the XO, it will be kept to support legacy data...?

(Was going to say that any datastore change must support the fact that
data will be on "old" USB sticks, but the Journal saves in a different
format to the USB stick.)

cheers,



m
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 martin at laptop.org -- School Server Architect
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