On Sat, Jun 26, 2021 at 8:36 AM Phil Turmel <philip@xxxxxxxxxx> wrote: > > You could lie to the firmware and tell it that each MD member device > > is an ESP, but it isn't. This will probably work as long as you use > > the correct metadata format (so the MD metadata is at the end and > > the firmware is fooled that the member device is just a normal > > partition). BUT it is in theory possible for the firmware to write > > to the ESP and that would cause a broken array when you boot, which > > you'd then recover by randomly choosing one of the member devices as > > the "correct" one. > > Pretty low risk, I think, but yes. If you construct the raid with what > the EFI system thinks as the "first" bootable ESP as member role 0, > mdadm will sync correctly. Fragile, but generally works. I think it's unreliable. GRUB can write to the ESP when grubenv is on it. And sd-boot likewise can write to the ESP as part of https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT/ And the firmware itself can write to the ESP for any reason but most commonly when cleaning up after firmware updates. Any of these events would write to just one of the members, and involve file system writes. So now what happens when they're assembled by mdadm as a raid, and the two member devices have the same event count, and yet now completely different file system states? I think it's a train wreck. -- Chris Murphy
