Corrected on Aug. 22. 2012
Thanks a seidler2547. Efectivily is posible to use sda3 partition on OMV only formating it.
We start from an OMV system running and installed on a hard drive that it could be /dev/sda and we want to use part of it as a aditional data storage unit for the system.
We stop orderly OMV, and with "gparted live" CD or USB (@ http://www.sourceforge.net
1) reduce the size of the partition /dev/sda1 (system partition) to a reasonable size, eg 8 GiB
2) extend the size of the primary partition /dev/sda2 to full disk size.
3) move the extended partition for swap, /dev/sda5 contained in the primary /dev/sda2, from the end, to the beginning of the /dev/sda2
4) reduce the size of the primary partition /dev/sda2 just to the size of the extended partition /dev/sda5
5) create a new partition with free disk size /dev/sda3
6) format /dev/sda3 with the type ext4
We stop orderly gparted.
We start again OMV and from the CLI we type:
and already, in "OMV web gui: raid" we find a raid like this:
openmediavault:100, /dev/md127, clean, linear, on /dev/sda3
We start again OMV and in the web gui we can look
storage:filesystems we find a line like this:
device /dev/sda3 filesystem ext4 Mounted no
we mount the device and wala....
Now, we can build on it shared folders and so on, all that we want and ......
Naturally, this configuration persists after stopping and starting the system