[LVM] Make it easier to fill the entire PV

[Daniel]

It's easy to believe that you actually get the full sized disk available to you after installation, and I find it confusing that you only get a hardcoded value once you run 'df' after the installation.

I suggest that we do it like you (Michael) suggest here: https://github.com/CanonicalLtd/subiquity/pull/737#issuecomment-682197172

In other words, make it easier to fill the PV during installation with an option like "Fill the entire PV" or something like that (needs better wording).

Thanks!

[Nobuto Murata (nobuto)]

Yes, the current behavior is confusing regardless of the good will behind it. The UI doesn't mention the fact that the installer doesn't use the entire disk with the root LV while it just says "use an entire disk" with 480GB (which will end up with 200G LV actually).

The UI text needs a face-lift with allowing to use (truly) entire disk and explaining the current behavior to set the proper expectation.
https://github.com/CanonicalLtd/subiquity/blob/fe012f20dc758f1fb1641d0b5744baf00739524d/subiquity/ui/views/filesystem/guided.py#L115-L173

[Konrad (kjoatmon)]

I agree that the LVM install options are very confusing and poorly described. Here is my experience, which shows one reason why more options are needed.

I recently made a new server. Normally I used to do centos, but I was not happy with some changes they made so I went back to debian a couple years back and now I need a new server. This time I decided to try Ubuntu Server 22.04 and in the install I ran into LVM. First time seeing it so I did a quick look as to what is was. I do not change/add servers a ton, so other than regular patches looking into things only happens when needed. Thus, I took ten minutes to "learn" LVM.

In short, I saw LVM as a way to add space later if needed without a lot of hassle. One of the primary features described in a simple search was the ability to extend file systems over multiple volumes at a later date, without reconfiguration, etc. This is a file and backup server I am replacing in a small office, so that sounded perfect. I could start with the machine we recycling from a front office desktop with a new hard drive. Then, at a later date, add or extend as needed.

In the install, I used the full drive. Not being familiar with LVM, I did not mess with the options. Every other "full drive" I have ever used from TRISDOS 1.3 and IBM DOS 2.1 as a teen until now has used a term along the lines as full or whole drive to mean the active use of the entire thing. This was why I was very surprised when moving files onto a 1TB server from a 512GB server that I ran out of space! Some digging and I finally figured out I had 100GB available for the root, not 900 some odd! I was able to extend with two commands, but it took me by surprise.

Now, I agree that the idea of allocating some space to virtual disks for other uses is valuable. LVM offers some wonderful solutions for that. However, they are options. Just like using LVM to make upgrading space easier is an option. The initial installer should, IMHO, adapt to the user's options via choices.

I think offering three default choices plus custom one step into LVM would be good. Something along the lines of:
1) Minimal system use, most space reserved for virtual disks to be added later. [This would be the current method.]
2) Balanced system use, half of drive reserved for virtual disks to be added later.
3) Full system use. No reserved space.
4) Custom, input % to be reserved for virtual disks to be added later. [Probably needs a maximum % shown as some will be needed by the system.]

Others have talked about other examples that they feel represent how it should be done. I have not looked at them. What I can say is that the present method of showing it to people assumes that they are 100% familiar with LVM and that they are not someone tossing together a low cost server for a home or business with an old machine and LINUX to eliminate license fees because the boss is looking at the economy and saying, "Do it as cheaply as possible," while the present server tosses out a BIOS error on boot and has some blown caps.