LaCie Ethernet Disk RAID (Firmware version 1.4)
User Manual
page 132
RAID and Storage Policies
10.2. RAID 1
Mirroring and Duplexing
Also called mirroring, this level makes a duplicate
write on a second or “mirror” disk every time data is
written to a primary disk. If one disk crashes, there is an
ideal backup (Fig. 7.2.A.).
Using two controllers, or duplexing, can speed the
data I/O rate by writing to both drives at the same
time. When using just a single controller operations are
slowed because data is written first to the data drive and
then to the mirrored drive.
e storage capacity of a two-disk RAID 1 array is
equal to the storage capacity of a single disk because the
same data is duplicated on both disks. However, the 100
percent redundancy of data does not require a rebuild
in the case of a drive failure. In that case, data can be
copied to a replacement disk.
Characteristics and Advantages■
Can sustain multiple simultaneous drive failures
in most cases
Simplest RAID storage subsystem design
Transfer rate for each block is the same as that of
a single disk
Data is 100 percent redundant
❖
❖
❖
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A
B
C
D
A
B
C
D
E
F
G
H
E
F
G
H
CONTROLLER
D
E
C
B
A
This diagram represents a
RAID 1 array, consisting of
four disks, which are
connected to the Controller.
Data blocks are duplicated,
or mirrored in each pair of
disks in the array.
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