Answering the OP question in case it helps anyone…
Since 2019, at my home, I have reliably run an ancient (2016-era) ASUS RT-N66U (32MB Flash & 256MB RAM) with a 4TB USB-powered HDD attached, until last month (10/2025) when I decided to upgrade to a used ASUS RT-AX3000 (256MB Flash & 512MB RAM). Unlike my ancient ASUS RT-N66U, I did not have to install Entware nor add USB swap-space to my RT-AX3000. I simply attached my 4TB USB-powered HDD, and the RT-AX3000 worked out of the box, perfectly fulfilling my 2 primary NAS/media-server needs. (1) The SMB/Samba server enables my family to do nightly PC & Mac backups, and store other files on the 4TB HDD. (2) The Mini-DLNA UPnP media-server enables us to easily stream HD movies and HD family-videos to our devices (mostly to our smart-TVs & Firesticks running Kodi & VLC), and lets us stream our mostly FLAC (220GB, 21,000 song) music collection & playlists to our app-controllable Yamaha networked receivers. The ASUS RT-AX3000 does everything that I want for NAS SMB/Samba & media-serving, so I have no desire to spend money and electricity on a separate NAS (though I understand and appreciate that others have greater NAS needs than me). Even my techie friends are impressed when they visit my Silicon Valley house that I can stream any downloaded movie, family video, song, album, or playlist to any of my TVs, stereos, PCs, phones, etc. And many of them ask me how they can implement the same NAS/server functionality. If more people knew how well this built-in NAS/server functionality works out of the box, then many more people would implement and love the functionality like I do… at least for ASUS routers. Speaking of which…
Before I bought the ASUS RT-AX3000, I bought a used TP-Link AX3000 “Archer AX55” (128MB Flash, 512MB RAM), but its NAS functionality and media-server functionality were abysmal. It could only see and serve (by SMB or its media-server) a small portion of my files even though its hardware is capable. TP-Link’s SMB & media server software is awful with very few options. I won’t buy another TP-Link router, and I will probably only buy ASUS routers from now on, mostly because I know for certain that I their NAS/server capabilities are adequate for my needs.
I can't say for certain which ASUS routers can handle my kind of NAS/server requirements, but I'm guessing that any ASUS router (with a USB port and USB-server functionality) that is at least as capable as the AX-3000 should be up to the task. I suspect that any ASUS router at the following ASUS website link that can have a maximum NTFS partition of at least 4TB would be OK, but I don't know.
