[Rear-users] New feature: savelayout and checklayout

Gratien D'haese gratien.dhaese at it3.be
Thu Dec 16 20:10:13 CET 2010

On 16 Dec 2010, at 16:15, Schlomo Schapiro wrote:

>> I know It's a major change, but perhaps you're interested in it and
>> see a way to move things further.
>> For code: https://code.launchpad.net/~jeroen-hoekx/+junk/rear-layout
> I think we would be very interested to enable ReaR to have several
> recovery strategies:
> 1. if the system is precisely like the original -> current code with
> vgcfgrestore
> 2. if the system is different -> new code with layout file and automatic
> guessing and user verification
> 3. if the system is slightly different -> new code with layout file,
> automatic guessing and no user verification (e.g. disk sized slightly
> different due to new model, new RAID ...)
> The user should be informed that the layout-based code can handle only
> simple LVM setups.
> Would you mind building a patch for that? I would also be happy to see
> the following changes to be part of that:
> * savelayout functionality part of dr stage (and thus called for each
> mkrescue/mkbackup run)
> * savelayout workflow is IMHO not really required any more because one
> MUST create a new rescue media if the layout changed. checklayout could
> be converted into an option of mkrescue like this (and this would make
> the cron jobs even simpler):
> ** rear mkrescue --quick (and keep the ISO somewhere and give the old
> ISO to the user if the layout did not change)
> ** rear mkrescue --onlyifchanged (and do nothing if the layout did not
> change, but how to report to the user that it is not an error that we
> did not produce a new ISO?)
> ** The code to pass args into the workflow is already there :-)
> * verify stage should decide if old or new code is used
> * verify stage should ask the user to approve the new layout (if
> approval is necessary)
> * recreate stage should recreate stuff with old or new code (IMHO this
> could be put into each script with an if $LAYOUT then ; new code ; else
> old code ; fi clause). Please rearrange the scripts in recreate stage if
> you believe they need to be rearranged.
> A patch like that would be most welcome. If you want to send me a
> working copy instead of a diff (to better track major changes and
> renames) this can be also arranged.
> If we see that the new code performs as well as the old code we could
> then switch the defaults or maybe fall-back to the old code for complex
> LVM setups that the new code cannot handle (yet).
> What do you think?

I'm not too fond of skipping parts of the mkrescue flow as it will lead to
situations that the code doesn't match the ISO, layout or whatever.
rear isn't run 10x a day so what does it matter it runs 1 minute longer
to generate an ISO image?
However, I do agree that the savelayout workflow should become part
of dr, but it may stay a separate flow too for me. If an admin wishes to run
it it should be possible.


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