Backing up your Raspberry Pi system disk to another SD card

To copy (backup) the disk you are running on to a better micro-SD card:

Put a high endurance micro-SD card (that is at least as large as the one you are now using) into a micro-SD card reader. Plug it into a USB port on your Raspberry Pi. Type lsusb. It should display something like

Bus 002 Device 003: ID 0781:cfcb SanDisk Corp. SDDR-B531
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 009: ID 1a2c:2124 China Resource Semico Co., Ltd Keyboard
Bus 001 Device 008: ID 046d:c52b Logitech, Inc. Unifying Receiver
Bus 001 Device 007: ID 1a40:0101 Terminus Technology Inc. Hub
Bus 001 Device 003: ID 051d:0002 American Power Conversion Uninterruptible Power Supply
Bus 001 Device 002: ID 2109:3431 VIA Labs, Inc. Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

SanDisk Corp. SDDR-B531 is the micro-SD card reader.

Then

startx  (If you aren't already in the GUI)

Accessories/SD Card Copier

(If you don't see "SD Card Copier" then you need a newer version of the Raspberry Pi OS.) Copy From Device" should be something like SH32G" (dev/mmcblk0) (This is your boot disk that you want to clone to a blank card.)

"Copy To Device" should be SanDisk SDDR-B531 Or whatever reader showed up when you did 'lsusb'.

Then click on the "Start" button

Wait until it is done. After it is done you can test the SD by powering down and swapping the newly created disk with your Pi's boot disk. Then power up. It should boot like it always did. You might be able to use the new boot SD in a different model Pi. This has worked in all the Pi I have (Zero W, 3B, 3B+, and 4B) but isn't guarenteed to work.

To copy one Pi boot SD to a different SD

To be safe use a full size reader and put the micro-SD you want to clone in an adapter and slide the write-protect switch to "lock" so you can't copy a blank SD onto your source SD. Put the SD card adapter in the reader. Put the (blank?) destination micro-SD in a different model reader (so you can tell them apart!) Plug the reader that has the source SD in (use the USB3 ports if a Pi 4 (or greater)). Type lsusb and note the name of the reader. Now plug in the reader that has the blank SD. Do `lsusb again and note the name of the 2nd reader that holds the blank SD.

startx  (if needed)

Accessories/SD Card Copier

Make sure that you are straight on "Copy From Device" (source card) and "Copy To Device" (unformatted blank SD card). (Putting the source disk in a write-protected SD adapter should protect you from overwriting the source SD. But still...

Is what I see when I clone from my SanDisk SDDR-C531 full size SD reader to my micro-SD Sandisk SDDR-B531 reader.

Then press "Start". It will take at least a few minutes to do the copy (faster if you use USB3 ports.)