An aggregate or traditional volume is comprised of one or more RAID groups. A RAID group consists of one or more data disks, across which client data is striped and stored, plus one or two parity disks.
When Data ONTAP's WAFL file system writes data to an aggregate/volume, the data is striped across the data disks in the RAID group(s) and parity is calculated and written to the parity disks. This allows for increased performance as all available disk spindles in the aggregate/volume's RAID group(s) are used.
Also check the Kb 3011896 " How does WAFL and striping distribute data among disks" for more information.
Hope this helps.
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