With Isilon you don't setup raid groups.  Rather it's a scale-out architecture.  You have individual nodes.  Each node will have X amount of drive slots depending on the type.  You have three possible node types: NearLine, Performance, and x200. Each node type have different attributes: Nearline is cost effective archive, performance is for speed, etc. Each node is part of a cluster.  Each cluster can support multiple node types. Each cluster has a disk pool for ever node type.  You need at least three nodes of the same type to form a cluster to maintain the defaultprotection level of n+1.  All capacity of all nodes is combined into one large filesystem called /ifs.  This filesystem is then exports out via NFS, CIFS, or (eww) iscsi.   For instance cluster may have 3Near Line (NL) nodes each with 36 1TB drives for a usable capacity of around 32TB per node (or 95TB for nearline diskpool), It may also have 4x200 type nodes each with 12 hard drives for storage and some SSD for metadata for a total capacity of around 70 TB in the x200 disk pool.  The total size of the cluster (/ifs) would be 95+70 = 165TB.  Data can then move between the nodes based on performance rules you define specific to your needs.  Hope that helps.
Boss wanted to know, and I am not sure how to.  RAID groups were easy to size up.  Cant find anything yet on how to do this with OneFS.  1Gazzillion points to person who answers this correctly before my Isilon tech calls back.  [IMAGE]
How do you calculate usable capacity for Isilon?