QNAP Security VioStor CMS (Version: 1.0.1) - Manual (Page 173)

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RAID 5 Disk Volume
The data are striped across all the hard
drives in a RAID 5 array. The parity
information is distributed and stored
across each hard drive. If a member
hard drive fails, the array enters
degraded mode. After installing a new
hard drive to replace the failed one, the
data can be rebuilt from other member
drives that contain the parity
information.
To create a RAID 5 disk volume, a
minimum of 3 hard drives are required.
The storage capacity of a RAID 5 array is
equal to (N-1) * (size of smallest hard
drive). N is the number of hard drives in
the array.
RAID 6 Disk Volume
The data are striped across all the hard
drives in a RAID 6 array. RAID 6 differs
from RAID 5 that a second set of parity
information is stored across the member
drives in the array. It tolerates failure of
two hard drives.
To create a RAID 6 disk volume, a
minimum of 4 hard drives are required.
The storage capacity of a RAID 6 array is
equal to (N-2) * (size of smallest hard
drive). N is the number of hard drives in
the array.