[CentOS] LVM hatred, was Re: /boot on a separate partition?

Tue Jun 23 18:23:52 UTC 2015
Mauricio Tavares <raubvogel at gmail.com>

On Tue, Jun 23, 2015 at 1:54 PM, Marko Vojinovic <vvmarko at gmail.com> wrote:
> On Tue, 23 Jun 2015 11:15:30 -0500
> Jason Warr <jason at warr.net> wrote:
>> I'm curious what has made some people hate LVM so much.  I have been
>> using it for years on thousands of production systems with no issues
>> that could not be easily explained as myself or someone else doing
>> something stupid.  And even those issues were pretty few and far
>> between.
>> /opens can of worms
> Well, I can only tell you my own story, I wouldn't know about other
> people. Basically, it boils down to the following:
> (1) I have no valid usecase for it. I don't remember when was the last
> time I needed to resize partitions (probably back when I was trying to
> install Windows 95). Disk space is very cheap, and if I really need to
> have *that* much data on a single partition, another drive and a few
> intelligently placed symlinks are usually enough. Cases where a symlink
> cannot do the job are indicative of a bad data structure design, and
> LVM is often not a solution, but a patch over a deeper problem
> elsewhere. Though I do admit there are some valid usecases for LVM.
      AIX does use lvm a lot. Main difference is their filesystem
allows live shrinking. Kinda nice to dynamically size a partition
depending on needs, as opposite to the so often suggested approach of
formatting the entire drive as one single partition. Symlinking is
great until whatever the destination is does not mount. I myself use
lvm as disks for my vm clients, which xenserver does too (not my fault
I promise!). It is faster than an image file.

> (2) It is fragile. If you have data on top of LVM spread over an array
> of disks, and one disk dies, the data on the whole array goes away. I
> don't know why such a design of LVM was preferred over something more
> robust (I guess there are reasons), but it doesn't feel right. A bunch
> of flawless drives containing corrupt data is Just Wrong(tm). I know,
> one should always have backups, but still...
      Building a raid0, which is what your example is, and hoping data
will survive in case of a drive failure is wishful thinking. You can
build VLM on the top of a proper raid, or do raid inside lvm
nowadayas... just like zfs,

> (3) It's being pushed as default on everyday ordinary users, who have
> absolutely no need for it. I would understand it as an opt-in feature
> that some people might need in datacenters, drive farms, clouds, etc.,
> but an ordinary user installing a single OS on their everyday laptop
> just doesn't need it. Jumping through hoops during installation to
> opt-in LVM by a small number of experts outweighs similar jumping to
> opt-out of it by a large number of noobs.
      That is not lvm's fault, but the distro's decision.

> Also, related to (3), there was that famous Fedora upgrade fiasco a few
> Fedora releases back. It went like this:
> * A default installation included LVM for all partitions, except
>   for /boot, since grub couldn't read inside LVM.
> * Six months later, the upgrade process to the next release of Fedora
>   happened to require a lot of space in /boot, more than the default
>   settings.
> * The /boot partition, being the only one outside LVM, was the only one
>   that couldn't be resized on-the-fly.
> * People who opted-out of LVM usually didn't have a reason to create a
>   separate /boot partition, but bundled it under /, circumventing the
>   size issue in advance without even knowing it.
      Fedora != lvm unless I have been lied to all these years.

> So the story ended up with lots of people in upgrading griefs purely
> because they couldn't resize the separate /boot partition, and it was
> separate because LVM was present, and LVM was present with the goal of
> making partition resizing easy! A textbook example of a catch-22,
> unbelievable!!
> Of course, I know what you'll say --- it wasn't just LVM, but an
> unfortunate combination of LVM, limitations of grub, bad defaults and a
> lousy upgrade mechanism. And yes, you'd be right, I agree. But the
> bottomline was that people with LVM couldn't upgrade (without bending
> backwards), while people without LVM didn't even notice that there is a
> problem. And since hatred is an irrational thing, you need not look any
> further than that. ;-)
> Best, :-)
> Marko
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