NAS with expandable RAID 5 and rsync

[danysk]

Hi everybody,
I just bought some cloud space where to backup my files, however, I also want a copy of them to be safely stored at my place.

I already have a 2TB disk and two 1TB disks. The plan would be to buy a new 2 or 3TB disk and put them in RAID5. I know I'm going to waste a lot of space right now, but the idea is to replace them "gracefully", one by one, when I'm close to run out of space. I would like to be able to replace a disk with a larger one and (if all the disks are bigger than the smaller of the initial configuration) expand the RAID without destroying it.

I am not very interested in high performance, achieving a 15-20MB/s write and 30-40MB/s read would be more than enough: the most stressful operation I could need is a 1080p movie streaming on 1Gbit LAN.

Summing up, the features I need are:
4 bays
Rsync cronjobs, possibly configurable via web admin. I want to run a "pull" and a "push" from/towards my cloud storage space, so that if I put new file on the NAS they will eventually be available online and vice-versa
SFTP
HTTP
1GBps network
Hot-swap
RAID5 expansion

Is there any product you recommend me? This would be my first NAS, so it's a bit difficult to choose the right one. I was evaluating the NETGEAR ReadyNAS RN104.

Thank you in advance for any help, cheers from Italy.