32 bit: mdadm gives error "blockdev: IOCTL-Fehler bei BLKGETSIZE: Die Datei ist zu groß" for each disk and does not assemble raid

[Michael Soegtrop]

I first asked this as question on Ask Ubuntu here:

https://askubuntu.com/questions/1372726/mdadm-raid-wont-assemble-after-update-from-16-04-lts-32-bit-to-18-04-lts

Essentially I upgraded a RAID server from Ubuntu 16.04 LTS to Ubuntu 18.04 LTS (both 32 bit). After that the RAID won't assemble any more and mdadm does not seem to detect any disks - see the above Ask Ubuntu question for logs and other details.

I then installed Ubuntu 20.04 64 bit on the same machine, and everything wokred fine. Since 16.04 32 bit and 20.04 64 bit work in the same configuration on the same machine and 18.04 LTS 32 bit doesn't, one can assume that 18.04 LTS 32 bit has an issue.

Interestingly, when I reinstall mdadm via apt-get, I get the following error once for each RAID disk:

"blockdev: IOCTL-Fehler bei BLKGETSIZE: Die Datei ist zu groß"

which is German for : "blockdev: IOCTL-Error at BLKGETSIZE: The file it too large"

I guess some variable which should be 64 bit in 32 bit Ubuntu is 32 bit.

Is it possible that mdadm is generally broken on 32 bit Ubuntu 18.04 LTS?

[Michael Soegtrop (msoegtrop)]

One more data point on this: 32 bit Debian 11.1 works fine on the same machine, on which 32 but Ubuntu 18.04 doesn't.