Expand RAID5 virtual disks on PowerEdge R720 with CentOS

Hi all,

I've added extra physical disks to my array using OMSA and everything went well up to this point:
 reconstruction ended and OMSA tells me the correct size for my virtual disk.

But now I have to tell CentOS that the partition should be extended, but it seems that CentOS is not aware of this new size. This is what i get when i call the print command in parted (the new size should be 4TB instead of 2TB) :

GNU Parted 2.1
Using /dev/sdc
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print
Model: DELL PERC H710P (scsi)
Disk /dev/sdc: 1999GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system  Name  Flags
 1      17.4kB  1999GB  1999GB  ext4

My question at this point is the following: the disk size given by parted (1999GB), is it the "physical" size it sees as available or the current size of the disk ? I believe it's the first case, so I haven't tried to resize it yet (the disk application with GUI tells me the same, so I'm not sure that formating it would let me use the new disk space)

Also, I have another virtual disk to expand, I'll do it when later when my current problem is solved. On this one, I'll had much more disk space and the reconstruction will be much longer. I read that reconstruction can be done while the server is being used but with "decreased performances" and I'm running a big application on this server. Is it recommanded to turn it off during the reconstruction ?

And finally, on that other VD I'll probably change the RAID type from 5 to 6, I'm sure it won't be a problem with OMSA but if there's anything I should know about it, the sooner the better :)

Thanks for your help !