volume expansion

norbert wrote:
Another question before purchase of ultra 6" Can I start with 2 disks and keep adding more in the future?

Yes. Take a look at X-RAID2 in Action

norbert wrote:
Would volume expand automatically?

Using the default X-RAID2 yes.

norbert wrote:
Also do I have to keep disks of the same size?

No. You can add higher capacity disks if you like. Using single-redundancy once you've added two higher capacity disks you'll get vertical expansion (utilise additional space on the disks over lower capacity ones). If using dual-redundancy you'd need to add four higher capacity disks.

Edit: of course if adding disks to empty drive bays (not replacing existing disks) you'd still get horizontal expansion (treating disk as same capacity as lower capacity disk) regardless of whether you add enough to get vertical expansion.