Filesystem other than the defualt?

my device is wrt1200ac linksys

can I install a filesystem other than the SquashFS and JFFS2?
if my device have more space than say 32MB but still on NAND( i am not sure if it is nand or not)

should everyone that uses NAND and not ssd or hdd always use SquashFS and JFFS2?
even if in theory that NAND has a lot of space?

if I want to use ext4 for my device ,is that a bad idea?
because of space or because of flash wearing or something else?

Sorry if this is a noob question.

You have 2*40 MB for kernel and rootfs, 36 MB for the rootfs alone, of which around 32-33 MB may be free space after installing a release image; that's it.

Your filesystems are squashfs+ubifs on ubi, you can't change that (unless you really know what you're doing, in which case you wouldn't touch it).

Keep in mind that your NAND has a limited amount of read/ write cycles, it's not meant for large amounts if volatile data - and 40 MB are plenty for OpenWrt's software packages. If you need more than that or want to host volatile data, look into USB sticks (cheap to replace, if broken) or USB SSDs/ HDDs.

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so it is no longer jffs2 ? it is now ubifs? can you explain that?
on wiki it just say for raw flash nand. what does that mean? does that mean my device need to support it? and then what ? does it include the squashfs in the ubifs, as in inside of it like a packet? so it would be HW>> raw flash >> ubifs >>> squashfs , inside each other??
or ubifs is used instead of jffs2?

and it was just a noob question. sorry if it was way off.

btw is there a way to find the processes that write to the nand so I can move their files (logs and data and so on) to my attached USB-HDD?

I tried the usb-rootfs before but for the life of me I couldn't figure out how to do firmware update on it. if there is a way to install ROM updates (not normal packages update but whole ROM) on usb-rootfs then I will switch of course. My device has a two partition (two main partition for data (kernel and root)) and uses one for recovery (installs to the alternative one on every update) .
so I think even if on a normal device I could find a way to ROM-update the usb-rootfs, on my device it would be way harder.
Am I right?

I build my own image with imagebuilder and once in a while (every month or so as to not wear out the flash) install them. is that too much? I think I should change that to whenever I get low space instead because I have enough space on device for updates if I include all the apps I need in my imagebuilder image.

Most packages are optimised to place write intensive data in tmp.... ( not nand )...

inotifywait -r -m /tmp ( ram )
inotifywait -r -m /etc ( disk )

honestly though...... a simple overlay extroot takes care of all that stuff..... except maybe the graph or log data in /tmp.

overlay extroot? as I remember I had issues with update on that (firmware updates not app updates ofc) on my tplink router.
now my new router has alternative boots and I am trying to stick with the main way of installation because I have put my router in a not-easily accessible place and I like to do all the updates and so on remotely. and ext-root needs manual intervention if I remember correctly.