In the event I want to set up a RAID 1 mirror utilizing mdadm, is it needed to have a file system on the drives first? Reason I ask is my desktop which has RAID 1 (built from the alternate install CD) says both drives (via GParted) are EXT4, along with /dev/md0 which is the usable volume of course. I just set up my server, which is currently resyncing the drives now, but it too had a RAID 1 mirror. My drives were unformatted when I added them to the mdadm array via terminal. I had set them as unformatted + set the RAID flag via GParted on a LiveUSB session prior to starting the array build process.
That being said, I'm sitting here wondering - if mdadm basically clobbers the data on the HDDs during the rebuild process, how are my desktop RAID drives coming up as EXT4 when independently looked at? Likewise, does that mean my server will come up in GParted through a LiveUSB session as unformatted when I look at each drive independently since they were unformatted before I started? And lastly... does it matter?