local and local-lvm: why there are two stores and what each is for

The install finished, you opened the panel, and on the left sit two stores with very similar names. You cannot tell from the names which is which, because the names state the technology they use, not the job they do.

The real distinction is this: what they hold.

There are two kinds of content

Files. Installation images, backup archives, container templates. These are files that sit in a directory, have names, and can be copied.

Disks. The disks of virtual machines and the root filesystems of containers. These are not files you would browse; they are set aside as raw space.

The two jobs look alike but their needs differ. A file store has to be flexible; a disk store has to be fast and orderly.

The moment you say "the option is not there"

Every store declares which kinds of content it accepts. If you cannot see the store you expected in a list while creating a machine, that is not a fault: that store did not take on that content type.

Once you understand this, half of the panel explains itself. A missing option is always a matter of permission, not a hidden bug.

Three practical consequences

First: when one fills up, the other does not help. Machine disks fill the disk store, installation images fill the file store. The two are usually separate places; having room in one does not rescue the other. The sentence "there is space but the machine will not start" always has this behind it.

Second: the default install puts both on the same physical disk. So the installation images you downloaded, the backups you took and your machines' disks all sit together on the boot disk. They share that disk both in space and in wear.

Third and most expensive: a backup written to the same disk as the machine is not a backup. When that disk dies, both the machine and the backup go. The default layout makes this very easy to do, because that is the only store within reach.

Do not look at the store's name, look at this question

Ask a single question for each store: "if this disk dies, what do I lose?"

If the answer is "a few installation images, I will download them again", that store is a relaxed one. If the answer is "all of my machines", that is a serious place. If the answer is "my machines and my backups", then there is a design error there and it is the first thing to fix.

Answer that question once for each store; the layout writes itself.

What Atlas does

On the storage creation screen, Atlas does not ask about the technology first, it asks about the purpose: what will this store hold, archive files or the disks of machines? It shows the technical equivalent as a subtitle, so it gives the correct term to whoever wants to learn it, but you do not need to know that term in order to choose.

The reason for this is the subject of this article: the question in the user's head is not "which filesystem", it is "where will this thing go". The screen should ask that question too.

Choosing the location is built on the same logic: creating a new area in a pool is presented as a single concept, whatever the technology behind it. And before you confirm, a summary of what will happen is shown, because setting up a store is a decision that is troublesome to move later.