Alternatives to Windows Home Server Drive Extender?

As Microsoft is cutting support for Drive Extender in Windows Home Server v2 (Windows Server Codename Vail is the official name), what are the alternatives to Drive Extender on a self-built machine?

Requirements:

• Easily add or remove drives (to gain more space or duplication)
• Redundancy (either through duplication of chosed folders, or through something equivalent to RAID level 5)
• Easy to set up and use (so RAID is out of the question)
• Drive failure should leave data readable/recoverable on working disks
• Performance
• Support drives larger than 2TB (WHS v1 does not support this)
• Drives of different sizes
• Network enabled (SAMBA/CIFS)

What are my options?

Solution 1:

I just discovered greyhole

It's for linux but in my opinion it's better than DE (at least there won't be demigrator.exe trashing the HDDs 24/7 in a way that forces me to stop it in the peak working hours, or there will be latency problems in the LAN when accessing files...)

And Amanda can do the computer backups. I have no reason to buy WHSv2 anymore.

Edit: I found the perfect linux distro to replace WHS! Amahi has greyhole installed by default. (And also a lot of useless multimedia servers)

Solution 2:

Data Robotics will be very relieved that Microsoft is dropping Drive Extender, as the closest thing I know of that is anything like it is the range of Drobo devices. It's hardware and pretty expensive, but it fits all your requirements.

I've noticed that they are particularly popular with not-particularly-techy freelance creative professionals.