Installing Latest OpenWrt on old hardware

Hi, I have a D-Link DIR-615 rev E1. This a 4/32 device and the last supported release was 15.05.1. My model has spots on the board for a USB port that I can add. I only need to use this device as a repeater, but was wondering if it would be possible to install the latest version of OpenWrt IF I add external storage via the USB. I was wondering if anyone has experience installing on similarly old hardware and the general process to make an image for this router. I have used the image builder a little to tweak the installation on the device, but I don't have a lot of experience with OpenWrt (I have a lot of linux experience though). Thanks for any help.

The 4 MB of flash is one problem, the 32 MB of RAM is another. It sounds like you've got the skills for an "extroot" install, getting things to run stably within 32 MB of RAM is a more difficult problem.

With excellent and good-quality devices with 16/128 (flash/RAM) or more and current SoCs and wireless subsystems available new starting around US$20, that would be my choice over buying and soldering on a USB connector and buying a stick. Those parts alone are about half the cost or replacing it completely.

Yes, I figured as much. However, I was planning to do this more as an experience activity, and if I brick the router or damage the board I would just buy a newer 16/128 or better router. I have some old salvage USB connectors and small old flash drives, the only parts I may have to buy are the smt resistors as I don't have a lot of smt parts, but these are really cheap.

The only part I am not clear on is whether the info on building with extroot is still current (is 4MiB still feasible), how bad the performance/stability is with swap to extend the ram, and general pointers on how to go about porting the target profile to the latest version for the image builder.

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Horrible -- Most USB drives have their write speeds measured in single-digit MB/s

You'll want the full build system as the image builder doesn't let you modify any packages or the kernel, just assembles pre-built ones together.

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4/32 devices can be used with the latest versions mostly OK, provided that only basic routing functions are used.

I am using three of these devices: MR3040v2, tl-841v9 and tl-1043ndv1 on 19.07 build.

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I would suggest building 17.01 from source with whatever you can fit and not adding extroot. You probably don't have enough RAM to run the extra programs you would be able to install anyway.
See https://openwrt.org/docs/guide-user/additional-software/saving_space

19.07 may fit because they have included some of these space saving tricks by default. You will be able to add more software if you use v17 and remove what you don't need yourself.

It's weird that they don't build the tiny target. Maybe the problem is that not all 4MB of flash can be used on this device and nothing fits.

You're definitely looking at a custom build, but it can work for basic stuff. This is simpler than using extroot, which has the problem that the filesystem driver etc still must be in internal flash. Also its kind of pointless to have a bunch of large packages (VPN, etc.) stored in extroot but no RAM to run them on.

Do you need LuCI or can you live without?

Okay, thanks everyone for the replies. It seems the general consensus is that the extroot is not worth it. I'll probably look at flashing an updated version first then, and then decide if I want to go through the trouble of adding a usb/extroot for fun based on how things go. The router really only needs to support bridging and wireless (with 802.11k/v/r).

I like LuCI because I am lazy and like flashy displays, but it's not needed. Part of the reason I asked about extroot is to see if I could keep LuCI as I figured it's the easiest thing to ax to save space but it seems like the RAM is the bigger concern. My main gateway/router box is an old PC that has a bunch of NICs and runs dnsmasq, nftables, etc so I can configure things by hand if needed.

I'd recommend strongly against using v17. It's EOL at the point and will receive no further updates, security or otherwise, as I understand it. Spending a lot of time on v18 is marginal, as it is "maintenance only" and will be EOLed soon.

The ar71xx target has been deprecated for some time now, and, even on v19, will receive effectively nothing but kernel bumps. Unfortunately, it doesn't look like the DIR-615 has been ported to ath79 (probably because it is so resource constrained that nobody has felt the desire to do so).

Of the choices, personally, I'd go with ar71xx on v19 if I were to spend time with the device.

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