Software RAID support
Look on Wikipedia for a good explanation of what is a RAID.
It would be nice to have support for software RAIDs on ReactOS. A great performance boost on one of the most critical performance bottlenecks of computing nowadays, ReactOS should support for a start JBOD, 0, 1, 10 and )+1. After that RAID 5, and finally RAID 6.
Some people argue that 'a Software RAID will never be as good as a Hardware RAID'. But it all depends on the point-of-view. One can also argue that 'a Software RAID will always outperform a hardware-based one, given enough resources.'. Nowadays, a mid-range machine (Athlon 64 3000) would barely reach 30% CPU use when doing a big file transfer to a 4 disk RAID 5 on Linux. With escalating performance, dropping prices, and muti-core CPUs hitting the market, the performance hit will get lower, and you can't beat the price argument. RAID hardware is expensive, Software RAID is 'free' (after the cost of programming). But it all boils down to give more to the user, and they'll eventually choose us instead of them. :)
To manage RAID, ReactOS should use EVMS + LVM. EVMS being a great interface, and LVM giving the flexibility it has, they are the sensible choice to do it. Open Source OSs (ROS, Linux, BSD, whatever) should suggest EVMS as the default partition manager for new installs.
Look at the Wikipedia explanation of what LVM stands for.
With LVM you can among other things shrink, expand, join, mirror your partitions, without having to put your file systems/disks offline (if done right). Along with RAID and EVMS, they will make ReactOS' disk/file system management a tad better than Windows' one.