I just tried to update the routerOS firmware in one of my CRS309-1g-8s+in devices and it failed. Pulled out a serial connection to check it and it says the firmware is missing or corrupt. A couple web searches said I need to use NetInstall to recover over a network, got that connected and configured, downloaded the ARM package, and booted the router again. It finds the pxeboot/bootp server and transfers the firmware. It never manages to get that firmware installed correctly and cycle back through trying to make things work.
I think I was using RouterOS 7.21 longterm, but whatever the current long term might be as of today.
Through the serial terminal, I was able to get this to boot into SWOS so I am operational, but I still want to fix the RouterOS partition.
Do I need to go in through serial and format the partition, then use serial or netinstall to transfer the firmware again? Can it load the firmware from a FAT32 USB drive?
I think I might have this same issue with one of my CRS326-24s+4q+ devices too, I'll be able to work on that soon when I move my servers back to their home and it can have some downtime.
Netinstall, if it completes successfully, formats ROS partition and installs ROS image. Optionally it also keeps configuration. So no manual storage formatting is required.
Running netinstall application can be troublesome sometimes, but symptom is usually that device never actually connects the netinstall running on a computer. You did not write explicitly whether you actually used netinstall application or if you used a generic bootp server on your network. It has to be netinstall ... the procedure uses bootp to transfer the image but after thant netinstall app sends some commands to the router (to do the storage formatting, dump the ROS image, etc.).
If you actually user netinstall and it started to perform the required steps but it eventually failed, then it could be that flash storage somehow got damaged ... and in this case installing ROS won't be possible any more. And you should contact Mikrotik support directly (either e-mail or via ticketing system), they might be able to offer you some kind of solution.
I was using a Windows laptop, directly connected to the management port on the 309, removed all modules from the slots. Netinstall was running as admin, and the correct firmware (ARM) was selected. It connected, got the address I gave the device in Netinstall, and said transferring in the serial output. Then it starts the entire process again giving the no OS or corrupt error message. This device is only 3 years old, it shouldn't have a storage issue yet. And I do think I'm right that my 2 month old CRS 326 (mentioned above) had also crashed during an update, but I had to put it in service right away and SWOS was "good enough" for what I needed and it has been that way for 2 years.