At the time of writing, we have the following ways of creating a
filesystem in the wiki:

    anarcat@curie:help.torproject.org(master)$ git grep mkfs
    howto/ganeti.md:        mkfs /dev/vg_ganeti/srv-tmp &&
    howto/ganeti.md:        mkfs /dev/vg_ganeti/srv &&
    howto/lvm.md:    mkfs -t ext4 /dev/vg_ganeti/srv
    howto/new-machine-cymru.md:    mkfs.ext4 -j /dev/mapper/36782bcb00063c6a500000aa36036318d
    old/new-kvm-virsh-vm.md:mkfs.ext4 "$part1"
    service/ci.md:        mkfs -t ext4 -j /dev/sdc

Most of them use `-t ext4` instead of `.ext4`. I consider that to be
best practice, because it doesn't assume implementation
details (e.g. the existence of `mkfs.ext4`) in `mkfs`.

We especially do not, ever, use `-m` in the filesystem creation, let
alone with "zero percent". That feels like a bad idea in general: if
we run out of disk space, we have no emergency procedure to
recover. We should definitely avoid that: in some cases, we *may* want
to reduce the percentage from the default (5%) to something
smaller (say 1%, it even supports fractional percentages).

We should probably *always* use a journal as well, although by
default (in `mke2fs.conf`) the journal is enabled by
default (`has_journal`) is set, so it is really redundant nowadays.