Rudi Ahlers wrote:
Something else I just realized, dedicated NAS devices can rebuild the RAID system on the fly, and offer online RAID migration and expansion, load balance, and failover - how would one do these with Linux?
Look at the mdadm tools for raid. Rebuilding on the fly is no problem if your hardware supports hot-swap. Expanding is more complicated and if you mange it, you then have to separately grow the filesystem into the new space. LVM might be more useful for migration/expansion. If you need mirroring/failover between two systems, look at DRBD and heartbeat.
I believe openfiler uses the native linux tools with a management wrapper to integrate the steps - where nexentastor uses opensolaris/zfs where the concepts are integrated directly.