Re: why are / and /home the same filesystem?

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On Tue, Feb 8, 2022 at 6:30 AM Peter Boy <pboy@xxxxxxxxxxxxx> wrote:
>
>
>
> > Am 08.02.2022 um 12:11 schrieb Patrick O'Callaghan <pocallaghan@xxxxxxxxx>:
> >
> > On Tue, 2022-02-08 at 16:48 +1030, Tim via users wrote:
> >> You may actually want hard size limits on different partitions.
> >
> > You can still have this with subvolumes. See btrfs-quota(8).
>
> Yes, a sentence beginning with „You can have this with ….“ is probably true for every IT topic.
>
> The question is rather whether you can realistically have it in everyday practice.

Yes, (open)SUSE enables qgroups by default for years. Fedora doesn't
enable them, but it's worth checking out 'man btrfs quota'. They're
pretty cool, and the docs consider the dilemmas raised by snapshots,
and how that affects accounting. There are some performance concerns.
Desktop users don't need to worry about it, you can enable them, play,
disable them. The whole quota btree is removed, no residue remains on
the file system.


> Workstation WG made BTRFS default with F33. Even now with F35 one year later, where is easily accessible documentation for a user who wants to install Workstation? Neither the current Installation Guide nor the Administrator's Guide give any information about how to handle BTFRS. The complete text is up to date with Fedora 25 or perhaps a bit later, only minimally updated to subsequent versions.

?

https://docs.fedoraproject.org/en-US/fedora/f35/install-guide/install/Installing_Using_Anaconda/

Those are Fedora 33 screenshots. "btrfs" appears 34 times in the
document. There's an entire section on creating a btrfs layout.
https://docs.fedoraproject.org/en-US/fedora/f35/install-guide/install/Installing_Using_Anaconda/#sect-installation-gui-manual-partitioning-btrfs

Since I wrote up the lightweight changes for docs when btrfs became
the default, I'm aware that the documentation has weaknesses. It is
still LVM centric, and doesn't have hints for Btrfs nuances.

In particular, with how to get the installer to reuse the "home"
subvolume for the /home mountpoint. It is super easy to do, but
totally non-obvious. The part most folks run into is not reusing
"home" subvolume itself, which is just a matter of clicking on the
previous installation "home" and assigning it to the /home mountpoint.
But rather how to install to / because it won't let you reuse the
"root" subvolume. This is due to the installer requiring a new clean
filesystem for root. Ext4 and XFS require reformat, but Btrfs gets a
partial exemption. You don't have to reformat, but you do need a new
"root" subvolume, so you just create a new mountpoint with the +
button, specify the mountpoint as /, and leave the capacity field
blank. It'll add / mountpoint *and* create a new subvolume in the
process. You can either delete the old "root" subvolume, or keep it -
it's a matter of space available but as all subvolume share space it's
a pretty simple calculation whether you have room for it or not.


> And I see no Workstation doc listet on docs.fp.o, unlike the other Fedora editions, again, after a year.

1. https://docs.fedoraproject.org/en-US/docs/
2. click on engineering teams, https://docs.fedoraproject.org/en-US/engineering/
3. click on workstation working group,
https://docs.fedoraproject.org/en-US/workstation-working-group/


> And is there an adapted installation step in Anaconda to expose an option to set a max. limit (e.g. like to handle the root login - deactivated, key only, . . .) and probably some other valuable capabilities? I can’t remember to have seen something like that.

Workstation is a different installation experience than Server.
Workstation does a Live install, using rsync, and users are setup in
GNOME Initial Setup rather than in the installer.


> Therefore, a user is dependent on clear and informative terminology. And, well, sub-„volume“ after 32 Fedora releases has a specific meaning.

There are only so many words.

I'm reminded of the word "chunk". You see this word quite a bit in
computer storage. If you specialize in one thing or another, you might
get the idea that chunk is a specialized word that has a pretty
specific meaning. And then you're surprised when you come across that
same term in another context, it means something quite different.
Chunk in mdadm is what the SNIA dictionary calls "strip" or "stripe
element" [1] On Btrfs, chunk is a different thing entirely, there's no
SNIA equivalent term. So it's certainly easy to get confused when
terms get reused.


[1] can you believe those two terms are synonyms?[2]
[2] part of the problem might be the English language, really. If
you've ever been confused about strip and stripe [3], it's not you,
it's the words themselves.
[3] These two terms are not synonyms. [4]
[4] It really could make you a bit bonkers. I've really digressed now.

-- 
Chris Murphy
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