Re: Importance of LVM (was Re: Partitioning criteria revision proposal)

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On Thu, 2012-10-25 at 22:51 +0200, drago01 wrote:
> On Thu, Oct 25, 2012 at 10:26 PM, Adam Williamson <awilliam@xxxxxxxxxx> wrote:
> > On Tue, 2012-10-16 at 17:55 -0700, Adam Williamson wrote:
> >
> >> BTW, on the topic of LVM specifically (whose importance we still haven't
> >> really established): I did some archive-diving last week. We first went
> >> to LVM-by-default all the way back in Fedora Core 3. There were two
> >> reasons for doing this. The 'official' one was to make it easier to
> >> expand the capacity of a system simply by adding another hard disk. The
> >> less official reason was to get more testing of LVM, which was still in
> >> its infancy at the time. Ever since then, we've stuck with the default
> >> really just because it's always been there; until I started poking into
> >> it, no-one really had a story for why LVM was default any more.
> >>
> >> Neither reason really applies much any more. LVM is much more mature
> >> now, and in a way is yesterday's news, the Glorious Future maybe belongs
> >> to btrfs. And we've finally hit the point in history where most people
> >> don't run out of space on the hard disk that comes with their system,
> >> and even when they _do_ run out of space, it's usually not with OS data
> >> but with 'user data' that is much easier to spread across multiple disks
> >> without using LVM. So I'm not sure we really have a convincing reason
> >> any more to care especially about LVM.
> >
> > On this topic...Ric Wheeler came up with some fairly good arguments in
> > favour of keeping the LVM default and proposed it on the anaconda list
> > this morning (actually I think the post may not have been approved yet,
> > but it'll show up soon). Since we're post-freeze now I summarized the
> > debate into a bug report and nominated it for NTH:
> >
> > https://bugzilla.redhat.com/show_bug.cgi?id=870207
> >
> > I think it's still true to say that our *original* reasons for
> > defaulting to LVM don't really hold any more, but Ric made some pretty
> > decent *current* arguments for keeping that default until we switch to
> > btrfs-by-default.
> 
> What exactly does not hold anymore? Resizing partitions isn't that
> common and not the primary use of LVM (you can do it without it and
> most users won't).  

You can do it without LVM, but not as reliably (you're *more* likely to
get into trouble resizing a raw ext4 partition than an LV) and with more
limitations (the big one being you can't resize an ext4 partition from
the front: so if you have a disk with 10GB / then 100GB /home, and you
fill up /, you can't make /home smaller and use the additional space
for /, because it can't be contiguous. All you can do is create a new
partition after /home and bodge it up somehow, by mounting it as /var or
something; much messier).

'most users won't' is hard to prove but likely true, but then, *some*
users will, and isn't it nice that they have the ability to do it?

> It is still pretty much useless (as in the extra
> features won't be used) for the average desktop / laptop installs.

They're neat features, though, and they're available, and _some_ people
can use them, and people who don't use them aren't hurt (except see
below).

>  For
> most users all it does is slowing down the boot process (we should
> stop adding crap to the default boot process because someone might
> need it on some obscure case). 

Does LVM slow down boot significantly? Do you have numbers for that? I
hadn't heard that factor cited in the debate so far. Could you add it to
the bug if you have solid data? It'd be useful input.

> Those who know about the extra features
> and want to use them will enable it anyway regardless on what we set
> as defaults.

It's somewhat harder to change in newUI than oldUI because there isn't
just a checkbox for it, and I don't think the designers want there to be
one. To change from the default (whatever the default is) you have to go
through custom partitioning.

Also, this doesn't catch the case of someone who's never used LVM, does
an install of Fedora, notices that it uses LVM, and gets interested
about it and finds out the neat stuff it can do. That's not a terribly
unusual use case for Linux distros in general, is it? We all start out
as newbies after all...I often find out about cool stuff 'by accident'
in this way, just by stumbling across it.
-- 
Adam Williamson
Fedora QA Community Monkey
IRC: adamw | Twitter: AdamW_Fedora | identi.ca: adamwfedora
http://www.happyassassin.net

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