[OT] info about filesystem directly on disk device and not partition

[Gianluca Cecchi]

Hello,
sorry for the off-topic.
Tipically when I work with LVM on Linux (RHEL/CentOS 5 and/or Fedora 11/12),
I create the physical volume directly on the whole disk.
Historically one created a partition on the disk, eventually big as the
whole disk and then marked it as 8e type (LVM), and then the PV on the
partition.
With recent kernels/LVM2 user tools it became safe/normal to create it
directly on disk device, and so I normally do.

What about same thing for ext3 filesystem?
So creating for example an ext3 filesystem directly on the /dev/sda device?
Does this imply any risk/problem?

Does it change anything if the underlying device is instead managed by
device-mapper-multipath, so for example the device name is
/dev/mapper/mpath1?

I ask because, used with creating PVs, VGs and LVs, today I had to create a
plain filesystem on mpath device and forgot to create a partition on it but
issued the mkfs command directly on it... and then mounted it... now I have
this doubt

Thanks in advance for any hints/ suggestions.

Gianluca