LVM is the Linux Volume Manager. In short it’s kind of like a partitioner inside the OS (but with lots of cool features, like encryption, snapshots and restores, and caches, RAID)
So you add all your drives, potentially with different groups like NVME, SSD. Then in those groups you create a volume (think partition).
Examples:
For example my laptop has one drive, and one volume group, but I have a separate volume for home so I can take snapshot (which are small if things haven’t changed much!) and keep my home direecty when installing a new distro. I also make a separate volume for a VM to keep my machine clean.
My server, however, has 2 NVME drives and 12 spinning rust drives in 3 USB enclosures. Each USB drive is set as its own VG. USB is slow though, LVM to the rescue.
I set the rest of the space on the 1st NVME and all the space on the 2nd NVME to work as a cache for each of the external enclosures.
Now writes are NVME speeds and it will write back to the spinning rust at USB speed. Reads from the usb enclosures if cached are at NVME If it’s in the read cache I get is at NVME speeds, otherwise it reads off the drive. At this point my read cache since creation is 82% and continuing to climb. So less than 1/5th of the reads actually went over the USB. At the rate it’s climbing the current hit rate must be in the mid to high 90s.
A pre-seed file is basically the answers to all the questions the installer would normally ask, like how to partition the drives, what mirror to use, software to install, settings to make, etc. default user accounts, etc. Now you can run that installer on a machine and walk away until it’s done.