Re: number of subvolumes

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> This is a vanilla SLES12 installation: [ ... ] Why does SUSE
> ignore this "not too many subvolumes" warning?

As in many cases with Btrfs "it's complicated" because of the
interaction of advanced features among themselves and the chosen
implementation and properties of storage; anisotropy rules.

IIRC the main problem actually is not with "too many subvolumes",
but with too many "reflinks"/"backrefs"; subvolumes, in particular
snapshots, are just the main way to create them:

  https://www.spinics.net/lists/linux-btrfs/msg42808.html

A couple dozen subvolumes without reflinks as in the '/' scheme
used by SUSE are going to be almost always fine.

Then there is different a issue: I remember seeing a post by a SUSE
guy saying that the 10/10/10/10 (hourly/daily/monthly/yearly)
snapshots in the default settings for 'snapper' was a bad idea
because it would create way too many snapshots, but that he was
told to set those defaults that high. I can imagine a cowardly but
plausible reason why "management" would want those defaults.

Some semi-useful links:

* Home page for 'snapper'
  https://snapper.io/
* Announcement of 'snapper'
  https://lizards.opensuse.org/2011/04/01/introducing-snapper/
* Useful maintenance scripts
  https://github.com/kdave/btrfsmaintenance
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