[SOLVED] what are all these partitions?

[oldgeek]

I've had to replace my motherboard, and the technician formatted my drive for me, probably expecting I'd install windows. I'm trying to do a manual install of Kubuntu 21.10 because I want to use btrfs, but when I get to the 'prepare partitions' dialog I'm amazed at the number of partitions. I don't remember having so many before. I can't take a screenshot of the setup, so I'll copy down what I see:

/dev/sda
free space -- 1 MB
/dev/sda1 ntfs -- 471 MB 324 used
/dev/sda2 efi --104 MB 33 MB used
/dev/sda3 --16 MB unknown used
/dev/sda4 ntfs -- 499513 MB 30484 used
/dev/sdb1 -- 3367 MB unknown used
/dev/2db2 -- 4 MB unknown used
free space -- 1 MB
/dev/sdb4 ext4 -- 4502 MB 155 used

Then below all that, under 'boot loader' it says the device for bootloader installation is /dev/sda

What do I have to do to install the OS under btrfs filesystem? What can I delete? How do I add the bootloader, and how much memory does it get?
I never expected this to be so complicated. Any help would be appreciated, as I'm absolutely stuck at the moment.

[jlittle]

...the technician formatted my drive for me, probably expecting I'd install windows

The technician set up the partitions on /dev/sda. /devsdb looks like an 8 GB USB stick, maybe the one you're installing from.

You need an EFI partition, and a btrfs one. As well, you may want a swap partition, as big as your RAM, if you want to suspend to disc; if you're not sure whether you need a swap partition, IMO you don't need it.

I'd make the EFI partition bigger, 500 MB, because it could conceivably be useful, and a few hundred megabytes is not very significant.

First I'd wipe the existing partitions on /dev/sda, then create an EFI one, then make a btrfs one taking the rest of the space. Mark the btrfs one to be used as "/". Ignore sdb, and I expect the installer will too.

[oldgeek]

Well, I did what you suggested, however I get an error message, but when I select Install shortly afterwards I get an error message 'The attempt to mount a file system with type SCSI4 (0,0,0) partition #1 (sda) at /boot/efi failed. If I continue the process, it seems to hang up with creating the btrfs partition at about 33% progress. What can I do?

[oldgeek]

UPDATE: I redid everything from scratch and, following jlittle's instructions, got the OS to install correctly. Now I'm just copying my backup home folder and am happy the problem was fixed so simply. Thanks, jlittle!