User manual

ERQ12-U4R2 & ERQ12-F2R2 Serial ATA Disk Array Systems
7
1 Overview – Understanding RAID
Summary of RAID Levels
The following table summarizes the performance characteristics of each RAID level. A high
availability or access rate number indicates high availability or quick access rate.
Array
Group
Availability
Access
Rate
Capacity
Utilization
Description
NRAID 1 1 100% Sum of all disks in the array
JBOD 1 1 100% Data is distributed by filling each
disk in turn.
RAID 0 1 5 100% Data is divided into pieces and
written to all disks in parallel.
RAID 1 5 2 50% Data is duplicated on both disks.
RAID 3 3 3 Between 67%
for 3 disks to
94% for 16
disks
Data is divided into pieces; the
parity of these pieces is calcu-
lated; and the pieces are written
to separate disks in parallel with
the writing of the parity to a dedi-
cated disk.
RAID 5 3 3.5 Between 67%
for 3 disks to
94% for 16
disks
Data is divided into pieces; the
parity of these pieces is calcu-
lated; and the pieces and parity
are written to separate disks in
parallel. The parity is written to a
different disk each time.
RAID 0+1 4.5 5 50% RAID 0+1 is a RAID 1 consisting
of RAID 0 members.
RAID 30 4 4 Between 67%
for 6 disks to
88% for 16
disks
RAID 30 is a RAID 0 consisting
of RAID 3 members.
RAID 50 4 4.5 Between 67%
for 6 disks to
88% for 16
disks
RAID 50 is a RAID 0 consisting
of RAID 5 members.