http://vstorage.wordpress.com/2010/04/05/the-new-networkraidfeatures-of-saniq-8-5/
Interesting new features, although seems complex
Prior to 8.5 you had the choice of Network RAID-10 with 2-way replica, 3-way replica or 4-way replica. i.e 2, 3 or 4 copies of your volumes distributed across the nodes for redundancy – the downside of this; decreased usable capacity.
8.5 introduces Network RAID-5 and RAID-6.
Network RAID-5 needs three data and one parity as a minimum configuration i.e 3+1 , meaning four nodes as a starting point.
Network RAID-6 needs four data and two parity as a minimum configuration i.e 4+2 , meaning six nodes are required initially.
Unlike Network RAID-10 which creates mirror replica(s) of a volume, the documentation states the new RAID levels stripe parity across all nodes in the cluster.
Network RAID–5 and and Network RAID–6 volumes require snapshots in order to achieve space utilization benefits.
This means that deleting the last snapshot of a Network RAID–5 volume causes its space requirement to be the same as a Network RAID–10 (2-Way Mirror) volume.
Similarly deleting the last snapshot of a Network RAID–6 volume causes its space requirement to be the same as a Network RAID–10+1 (3-Way Mirror) volume.
It is possible, therefore, for the storage cluster not to have enough space to accommodate the snapshot deletion.
Deleting the last snapshot of a Network RAID-5 or Network RAID-6 volume is not recommended.
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