Date: Tue, 17 Jan 2017 19:46:51 -0600 From: Brandon J. Wandersee <brandon.wandersee@gmail.com> To: Arthur Chance <freebsd@qeng-ho.org> Cc: FreeBSD-Questions <freebsd-questions@freebsd.org> Subject: Re: Boot environments and /var - what should be shared/unshared? Message-ID: <86h94xcf78.fsf@WorkBox.homestead.org> In-Reply-To: <c7e9a10b-4794-27af-27da-5a8e8c483aee@qeng-ho.org> References: <c7e9a10b-4794-27af-27da-5a8e8c483aee@qeng-ho.org>
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Arthur Chance writes:
> I've been using beadm boot environments for a while now, but still
> haven't seen a definitive reference for which parts of /var should be
> shared across boot environments and which should be per environment. Is
> there such a document, or is everybody still busking it?
>
> Some top level directories in /var seem fairly obviously in need of
> sharing, others less so, and /var/db seems to be a horrible mix of stuff
> that could be shared across releases and stuff that might break horribly
> if shared over major revisions. (That's "might" because I have no idea
> if it would in practice.)
>
> I doubt whether any of this would matter (except for space) if one
> simply rolled forward monotonically, but a roll back because of
> problems, or simply switching between development environments, could
> lose necessary updates if the directory hadn't been shared when it
> should have been.
I suppose I can't give you a "definitive reference," but I selected
things to omit from boot environments based on advice in the book
/FreeBSD Mastery: Advanced ZFS" by Michael W. Lucas and Alan
Jude. Here's what I've got, follow by the reasoning behind it:
| NAME USED AVAIL REFER MOUNTPOINT
| workbox/VARIABLE 3.82M 72.5G 144K none
| workbox/VARIABLE/crash 144K 72.5G 144K /var/crash
| workbox/VARIABLE/log 2.86M 497M 1.80M /var/log
| workbox/VARIABLE/mail 340K 72.5G 196K /var/mail
| workbox/VARIABLE/tmp 360K 72.5G 144K /var/tmp
1. /var/crash, /var/tmp: The contents of these directories are supposed
to store non-volatile data, some of which is
relevant to recovery. You don't want it
disappearing after a reboot, or want to have to
find and mount an extra ZFS dataset in order to
access it.
2. /var/mail, /var/log: Mail and logs are generated by applications as
well as the base system, and are
time-sensitive. You don't want these skipping
around through time at all, but it's more
egregious if you lose a day's worth of logs for
your web server because something in the base
system got messed up. That's exactly the sort of
thing the BSD filesystem hierarchy was designed
to prevent in the first place.
I've also got a couple datasets mounted in /var, but as children of
another tree:
| workbox/APPS 6.26G 72.5G 5.42G /usr/local
| workbox/APPS/config 7.17M 72.5G 6.22M /usr/local/etc
| workbox/APPS/pkgCache 238M 2.77G 236M /var/cache/pkg
| workbox/APPS/pkgDB 162M 72.5G 81.5M /var/db/pkg
This way I can roll back package upgrades all at once without touching
anything else on the system. I used to handle packages/ports within boot
environments, but decided to separate them once I realized that doing so
could make them grow pretty large with successive upgrades. Having your
ports/packages tied to boot environments is really only useful when
tracking -CURRENT or performing a major version upgrade, so I see it as
a waste to constantly take up space in preparation for something that
happens once every couple years, for which I'll have ample warning and
preparation.
Someone else might come along with better ideas, but I suspect a lot of
it depends on taste and personal need.
--
:: Brandon J. Wandersee
:: brandon.wandersee@gmail.com
:: --------------------------------------------------
:: 'The best design is as little design as possible.'
:: --- Dieter Rams ----------------------------------
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