Originally Posted by scientest
Could you explain the issue in English perhaps (pretty please)?
He would like to use FreeNAS, because the support for ZFS is better in FreeBSD (the OS FreeNAS is built on) is better than the ZFS support in Linux.
ZFS offers a wealth of features for software RAID arrays (called RAIDZ or RAIDZ2 for ~RAID5 & 6) - it is very low overhead, massively scaleable, offers automatic online de-duplication, etc...
However the one thing it can't do is expand an array. You can only add new sets of disks to an existing pool. In more 'RAID-like' terms you can't add drives to an existing RAID6 array like most hardware RAID cards can, but you can add a new set of drives and create a 'RAID60' array across them. The big advantage comes from the fact not all the RAID spans need to be the same size - so you can use 8x1TB drives for your first set of disks, then add 8x2TB drives, then down the line add 8x4TB drives and span across all of them. For a RAIDZ2 (RAID6) array you would lose the capacity of 2 of each drive set - and end up with 6x1+6x2+6x4=42TB raw capacity, all in a single array.
He is hesitant to use FreeNAS for his OS because he is not overly familiar with FreeBSD, and as a result doesn't want to have to perform data recovery with CLI tools on an OS he doesn't know inside out.
That's about what he was talking about (or my interpretation of it), whether or not it is any more in English or not is another matter...