[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

[Roberto Ragusa]

Gianluca Cecchi wrote:

>  So creating for example an ext3 filesystem directly on the /dev/sda
> device?
>  Does this imply any risk/problem? 
No, but BIOS or other operating systems could be a little confused.

>  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? 
No problem for me when using dm-crypt on entire disks.

-- 
   Roberto Ragusa    mail at robertoragusa.it

[Bruno Wolff III]

On Wed, Mar 24, 2010 at 09:44:36 -0700,
  Rick Stevens <ricks(a)nerd.com&gt; wrote:
>  
>  On the other hand, a partition table doesn't take any capacity away
>  from a drive so there's really no need to skip partitioning other than
>  laziness. :-)  (and yes, I can be a lazy cuss) 
This can make a difference for live usb devices. There is differing file
system support depending on whether syslinux or isolinux gets used. Notably
NTFS only works for one of the two. This is an issue when you want both
images over 4 GiB and Windows compatibility.

[Rick Stevens]

On 03/23/2010 03:55 PM, Gianluca Cecchi wrote:
>  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 
I've built filesystems (ext2 and ext3) for a long time on thumb drives
(and certainly on floppies) without partitioning, so yes, you can do it.

On the other hand, a partition table doesn't take any capacity away
from a drive so there's really no need to skip partitioning other than
laziness. :-)  (and yes, I can be a lazy cuss)
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