Actually, for 50Pb of space, an0n, you'd have to use XP64, Win2k64 or a *nix.

But that's pedantry.
For a beginner, Maeg, avoid RedHat. The RedHat package management is horrible, and they've done so many horrible things to the file system, that it would be hard to transfer your RedHat skills over to any other Linux based OS, let alone another Unix like OS.
I recommend Gentoo. Better yet, I recommend being utterly conservative and not using Linux at all: use FreeBSD. The hardware support is leading edge, not bleeding edge, so newer hardware may not be completely supported. But the hardware that is supported is supported very well. Further, the system as a whole is more stable, which means you spend less time trying to figure out if you broke something or if that thing was broken as designed. Package management and building from source go hand in hand, and installs are completely reversible. You don't get the same sort of thing with any of the Linux package managers (except maybe debian's apt or gentoos portage, which is just a rip of BSD's ports). Finally, you don't have to worry about the screw Linux bootloaders. LILO and GRUB both (yes, I know there's more, but they're all arguably worse than LILO and GRUB) are fragile. On the other hand, FreeBSD is quite happy to use the Win2k/XP bootloader if you desire, or provide its own, sane and dynamic bootloader.