LaCie Ethernet Disk RAID
User Manual
page
RAID and Storage Policies
10.3. RAID 5
Data Striping with Striped Parity
Like RAID 0, RAID 5 offers increased performance
by distributing the data across multiple disks. But unlike
RAID 0, RAID 5 also offers data protection. If your
Ethernet Disk RAID has three disks of equal size, two
thirds of each disk are used for data, and the remaining
third contains the parity information needed to recon-
struct either of the other two. In this way, if any of the
three disks fails, it can be reconstructed when a new disk
is installed in the Ethernet Disk RAID.
If your Ethernet Disk RAID has four disks of equal
size, three fourths of each disk are used for data, and
the remaining fourth contains the parity information
needed to reconstruct either of the other three. If any of
the four disks fails, it can be reconstructed when a new
disk is installed.
You can use RAID 5 only if your Ethernet Disk
RAID has at least three disks. If the disks are not the
same size, the smallest of the disks determines how
much disk space is available for data. For example, if one
disk is 300 GB, one is 400 GB, and one is 500 GB, only
300 GB from each disk can be used. Two thirds of each
disk (200 GB) is used for storage space, and the remain-
ing third is used for parity information. As a result, only
600 GB of disk space would be available for data.
CONTROLLER
D
This diagram represents
a RAID 5 array consist-
ing of four disks, which
are connected to the
controller. Three-fourths
of each disk is used for
data storage and the
other fourth holds the
parity information used
to reconstruct the other
three disks in case of
failure.
A1
B1
C1
P1
D2
D3
D4
P2
C3
C4
B2
P3
B4
A2
A3
P4
Fig. 10.3.
Recommended Uses
■
File and Application Servers
Database Servers
Web, E-mail and News Servers
Intranet Servers
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Characteristics and Advantages
■
Highest Read data transaction rate
Medium Write data transaction rate
High efficiency through a low ratio of ECC (Par-
ity) disks to data
Good aggregate transfer rate
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