In professional life I use Proliants with SmartArrays so everything just always works. I'm new to md so forgive me if I make some "newbie" suggestions.
First, I like it A LOT. As I told someone recently that wanted to know "why I bothered" to mirror boot & root: "If I have the luxury of reloading an OS from CD or alternate disk and then have the time it takes to configure it enough to restore a backup tape, then I can do the same with the user's data. To me ... without boot & root raid would be useless.
But Disk Druid needs to have a MUCH clearer understanding of what Raid is and how people use it. Four dives /boot & root Raid1 while /usr /var & /home are Raid5 ... can take you all night to set up and sometimes Druid gets so confused that Anaconda crashes. I have MANY Anaconda issues regarding Raid. Many crashes, many reformats ... many issues.
That said ... the md system itself ....
First, I'd like a monilithic config file. It seems that too many utilities pull too many things from different places. Then again, maybe it does and I just don't know. One day I'll Read The Friendly Manual.
Next, while GUI would be welcomed from an admin standpoint the priority use should be for monitoring. An Xterm graphical update of volume health that can be left on the desktop. While printing /proc/mdstat is OK ... it's impossible to tell someone ELSE what they're looking at if you have to lead them through it.
Next thing is .. WAY too many error messages stating "md: invalid raid superblock magic on /dev/md{whatever}" or "/dev/md{x} does not contain valid ext2 superblock" or other messages. Of those two ... why would anyone thing that the first was acceptable/normal but not the second?
Last -- what others have said -- I want raid for high availability, so it needs to bust it's buns to restart. If a degraded array won't start (btw that's news to me!!!) then it's not a degraded array, it's a broken array.
