10.3 zpool/var canmount = off?

Brandon J. Wandersee brandon.wandersee at gmail.com
Fri Sep 16 21:18:40 UTC 2016

Matthew Seaman writes:

> The point of having zroot/var (with canmount=off) that just acts as a
> placeholder is so that eg. zroot/var/log or zroot/var/tmp (which you'll
> see have 'canmount=on') get mounted in the right location in the file
> system without becoming part of any boot environment.  That means
> there's only one copy of those filesystems and it always gets mounted
> every time you reboot -- which is really what you want for eg. /var/log
> but not correct for boot environments in general.  Usually you'll have
> several available, but only one of them should be mounted and active.

Matthew covered all the big stuff, but the ability to create dataset
trees with non-hierarchical mountpoints, or an unmounted dataset as the
root of a dataset tree, is actually a very useful administration
trick. Boot environments are one example, but it also lets you manage
and easily roll back all parts of a system that are related to each
other, but the files for which are stored in different parts of the
filesystem. You could, for example, create a dataset tree for every
component of an Apache or Nginx configuration. I have a tree of
filesystems for everything related to ports/packages except distfiles,
so I can roll everything back in lock-step if an upgrade goes bad while
avoiding having to download everything again.

::  Brandon J. Wandersee
::  brandon.wandersee at gmail.com
::  --------------------------------------------------
::  'The best design is as little design as possible.'
::  --- Dieter Rams ----------------------------------

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