Zfs

On a UEFI Ubuntu system there’s a 123-byte file on the ESP that almost nobody looks at. Mine was at \EFI\ubuntu\grub.cfg and contained this: search.fs_uuid 0a9ccc8b-d14c-4291-9eb8-7bf71995a901 root hd2,msdos1 set prefix=($root)'/grub' configfile $prefix/grub.cfg That’s the whole bootstrap. The signed grubx64.efi on the ESP has no idea where your real configuration lives, so this stub finds the /boot filesystem by UUID, sets $prefix to point at it, and chains to the grub.cfg that update-grub generates. Three lines, and I’d never read them before the day my NAS stopped booting. ...

While rebuilding the root filesystem of my NAS I had to decide how much swap to give it. The machine has 128 GB of ECC RAM and runs a ZFS pool, some containers, and a Spark setup that occasionally gets greedy. The old install had a 976 MB swap LV that wasn’t even in fstab. The folk rule says swap should be at least as large as RAM, which would mean carving 128 GB out of a 929 GB mirrored volume group for something I’d hope never to use. That felt obviously wrong, so I went looking for where the rule comes from. ...