Originally Posted By: Archeon
I've read about dedicated NAS devices like the Synology CS-407 with which is possible to 'upgrade' a RAID5 array by replacing the disks one by one and having the array rebuilt after each disk replacement. (eg. You've got 4x 500 GB, and after you replace them with 1TB disks one by one, you'll end up with a 4 TB RAID 5 array, well 3 TB of usable space). Is this also possible with nowadays RAID hardware RAID controllers? Or even better maybe, has it become possible maybe to add an extra disk to the array when you're running out of storage space maybe? (that would be cool)


Every Smart Array controller in the Proliant server line has always supported both of these features, going back to the first card in 1995. So it's not new to RAID controllers, but it wasn't common on the workstation class RAID solutions until later. My ReadyNAS uses a hardware RAID controller, and also offers both of these features when using what they call X-RAID. Theirs is built around always allowing scalability, and picking the right redundancy at the right time. If you start out with one disk and enable X-RAID, it just shares it out normally. Add a second disk, and you now have RAID-1. Add a third, and the array is migrated to RAID-5. And now it looks like the X-RAID2 in the ReadyNAS Pro will go up to RAID-6 if you want it to.

Hardware vs software, I'll let the other people here debate that one. Going either way has risks and benefits unique to each, and generally either one can do well for performance and reliability.