GridRAID

Description of GridRAID and how it differs from MDRAID

GridRAID is a new Sonexion RAID level that combines the logical stripe structure of RAID 6 (8+2) data protection with the pseudo-random distribution of the RAID 6 parity groups along with reserved spare data blocks across many physical storage devices.

The primary difference between SSUs configured with MDRAID RAID 6 arrays and SSUs configured with GridRAID is the ratio of drives to OSTs and the number of OSTs per SSU. For MDRAID systems, each OSS typically operates using 40 drives configured as four (4) 8+2 RAID 6 arrays for a total of four (4) OSTs per OSS and eight (8) OSTs total per SSU. An additional two (2) drives are reserved as global hot spares for a total of 82 drives. With GridRAID the same 82 drives are configured as two 41 drive GridRAID arrays with no dedicated hot spare drives. Instead two (2) drives worth of spare space is distributed along with the 8+2 parity groups distributed evenly across all 41 drives in the array. Though this results in a decrease of one (1)-drive-worth of the physical storage allocated to the GridRAID array, the amount of reserved space is adjusted so that the real available storage space for each configuration is the same.