Fixed the link, even though is not super relevant now that I have the solution 
For future users, it is.
Can you share how you got this done? Mine is showing this,
cat /proc/mtd
dev: size erasesize name
mtd0: 00100000 00040000 "0:sbl1"
mtd1: 00100000 00040000 "0:mibib"
mtd2: 00080000 00040000 "0:bootconfig"
mtd3: 00080000 00040000 "0:bootconfig1"
mtd4: 00300000 00040000 "0:qsee"
mtd5: 00300000 00040000 "0:qsee_1"
mtd6: 00080000 00040000 "0:devcfg"
mtd7: 00080000 00040000 "0:devcfg_1"
mtd8: 00080000 00040000 "0:apdp"
mtd9: 00080000 00040000 "0:apdp_1"
mtd10: 00080000 00040000 "0:rpm"
mtd11: 00080000 00040000 "0:rpm_1"
mtd12: 00080000 00040000 "0:cdt"
mtd13: 00080000 00040000 "0:cdt_1"
mtd14: 00080000 00040000 "0:appsblenv"
mtd15: 00100000 00040000 "0:appsbl"
mtd16: 00100000 00040000 "0:appsbl_1"
mtd17: 00080000 00040000 "0:art"
mtd18: 06400000 00040000 "rootfs"
mtd19: 01880000 00040000 "0:wififw"
mtd20: 06400000 00040000 "rootfs_1"
mtd21: 01880000 00040000 "0:wififw_1"
mtd22: 00240000 00040000 "0:ethphyfw"
mtd23: 00100000 00040000 "0:board_data"
mtd24: 00800000 00040000 "0:arc_datadump"
mtd25: 2cbc0000 00040000 "0:arc_data"
root@Telstra_5G:~#
I have arc_datadump and arc_data partitions at the end, but I'd like to modify them like you did to gain access to more NAND storage
In your case flashing mtd18 should work, as it is marked as rootfs. That's all I did.
No, I think you have a different MTD partition layout. Flashing factory.ubi does not change the MTD partitions. Did you used any U-Boot mod?
Nope, this was out of the box - those commands were run though after stopping the boot via UART and starting from an vanilla openwrt initramfs.
There is one additional complication here. This is a dual-firmware device, but a single overlay cannot be shared between two different firmware installations (versions). Regardless of the question if OpenWrt can currently use the 'b' partition slot, that may be added in the future and cause problems.
I'm not saying that it can't be done, just that there are further considerations (including the question what use the partition has in the OEM firmware - and what the procedure would be to revert to OEM; the partition name does suggest some function, rather than just spare space).
it is possible to use rootfs_1 for another firmware right? seems like roofs_t is empty(0 ubi volumes). i tried flash factory.ubi into mtd 20(roofs_1) but luci app advanced reboot not detect this device is has dual firmware support.
GLM-4.5 LLM proposed to format mtd25 - arc_data and format with ubifs in order to be able to use these 680MB as overlay.
My question is that is arc_data partition actually unused? Is it safe formatting it?
Check this link
Thank you very much for the provided instructions. This new mtd layout makes our AW1000 a killer openwrt router.
Anyone know how to get sms working on openwrt aw1000? Thanks
As long as it supports your language, I don't know of a better package: