On Sunday, 30 November at 05:55, Peter via Dng wrote:

>From:    Steve Litt <slitt@???>
>Date:    Sat, 29 Nov 2025 21:58:28 -0500
>> ... Ext4 or btrfs etc is good enough for me.
>> ...
>> Let's say your boot drive is a single partition on an NVMe. You
>> install your OS on that, as THE single partition.

>
>Good tutorial. Thanks! Stored in the SteveLitt file here.
>
>(1) Often the orginal system is on /dev/sda. For blunder avoidance,
>will translate "/dev/sda" to "/dev/sd<somethingElse>" before messing
>with commands.
>
>(2)
>> The real beauty is when you add a few other directories, which
>> used to be mountpoints. Instead of you having to guess how much
>> they'll hold, you can just symlink them to corresponding directories
>> under /bindmounts, and you'll have former mountpoints that are now
>> completely expandable and shrinkable.
>
>Good.
>
>Suppose you add another device, /dev/sdb. You can't have a directory
>spanning /dev/sda and /dev/sdb. Correct?
>
>All I know about overlayfs is from Wikipedia.
>https://en.wikipedia.org/wiki/OverlayFS
>Reaches a result similar to yours? Allows a directory to span
>multiple devices? Another gadget to try when there's time to spare.
>=8~/

OverlayFS could indeed achieve the same effect, but it would be more
complicated that Steve's system.

An overlay mount on /home/bob requires at least one "lower directory"
which will be read-only. If /home/bob is to be writeable (I assume this
is usually going to be the case), the overlay mount also requires an
"upper directory" (which will be writeable) and a "work directory". None
of these directories can be /home/bob (that's the mount point), but can
be on different filesystems.
Even though /home/bob technically can span several devices, only one of
them will ever be written to.

There are also side-effects. For example, if a file is in a lower
directory, deleting it from the mountpoint directory masks it in the
upper directory, but doesn't truly delete it (it is still present in the
lower directory).

- Antoine

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