Re: subvols and parents - how?

[Christoph Anton Mitterer <calestyo@scientia.net>]

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On Fri, 2015-11-27 at 01:02 +0000, Duncan wrote:
[snip snap]
> #1 could be a pain to setup if you weren't actually mounting it
> previously, just relying on the nested tree, AND...
> 
> #2 The point I was trying to make, now, to mount it you'll mount not
> a 
> native nested subvol, and not a directly available sibling
> 5/subvols/home, but you'll actually be reaching into an entirely 
> different nesting structure to grab something down inside, mounting
> 5/subvols/root/home subvolume nesting down inside the direct
> 5/subvols/root sibling subvol.

Okay so your main point was basically "keeping things administrable"...


> one of which was that everything 
> that the package manager installs should be on the same partition
> with 
> the installed-package database, so if it has to be restored from
> backup, 
> at least if it's all old, at least it's all equally old, and the
> package 
> database actually matches what's on the system because it's in the
> same 
> backup!
I basically agree, though I'd allow few exceptions, like database-like
data that is stored in /var/ sometimes and that doesn't need to be
consistent with anything but iself... e.g. static web pages
(/var/www)... postgresl DB, or sks keyserver DB... and so on.

btw: What's the proper way for merging / splitting into subvols.
E.g. consider I have:
5
|
+--root (subvol)
   |
   +-- var (no subvol)

And say I would want to split of var/www into a subvol.
Well one obvious way would be with mv (and AFAIU that would keep my
ref-links with clones, if any) but that also means that anything that
accesses /var/www probably needs a downtime.
Is it planned to have a special function that basically says:
"make dir foo and anything below (except nested subvols) a subvol named
foo, immediately and atomically"?

And similar vice-versa... a special function that says:
"make subvol foo and anything below (except nested subvols) a dir of
the parent subvol named foo, immediately and atomically"?

Could be handy for real world administration, especially when one
want's
to avoid downtimes.

btw: Few days ago, either Hugo or your thought that mv'ing a subvol
would change it's UUID, but my try (which was with coreutils 8.3 -> no
reflinked mv) seemed to show it wouldn't but there was no further reply
then... so am I right that the UUID wouldn't change?


> The same idea applies here.  Once you start reaching into nested
> subvols 
> to get the deeper nested subvols you're trying to mount, it's too
> much 
> and you're just begging to get it wrong under the extreme pressures
> of a 
> disaster recovery.
Well apparently you oversaw the extremely simple and reliable solution:
leaving a tiny little note on your desk saying something like: "dear
boss, things are screwed up, I'm on vacation now..." ;-)


Thanks,
Chris.

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