I’m running extroot fr a uSD card on a Certa (GL-AR750; DDR2 128MB / NOR Flash 16MB, firmware 4.3.7-release4). After completely resetting the device to stock I only installed parted & the requirements for F2FS (see Using storage devices) as the minimum requirements. After a successful first boot, I set the mount delay to give a little extra time.
I’ll probably add atgc,lazytime to that mount point too as a little extra performance tweak to save some wear on the card.
root@certa:~# df -h
Filesystem Size Used Available Use% Mounted on
/dev/root 11.5M 11.5M 0 100% /rom
tmpfs 59.2M 2.0M 57.1M 3% /tmp
/dev/sda1 974.0M 180.4M 793.6M 19% /overlay
overlayfs:/overlay 974.0M 180.4M 793.6M 19% /
tmpfs 512.0K 0 512.0K 0% /dev
/dev/mtdblock6 1.8M 1.3M 492.0K 73% /rwm
[...]
uci set fstab.@global[0].delay_root="15"
uci commit fstab