LaCie 301161U - Ethernet Disk RAID NAS Server User Manual page 133

LaCie Ethernet Disk RAID
User Manual
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.
The 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.
(Firmware version 1.4)
RAID and Storage Policies
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
❖
This diagram represents a
RAID 1 array, consisting of
E
four disks, which are
connected to the Controller.
D
Data blocks are duplicated,
C
or mirrored in each pair of
B disks in the array.
A
CONTROLLER
A E E
A
B F F
B
C C G G
D D H H
Recommended Uses
■
Payroll
❖
Accounting
❖
Financial
❖
Any use that requires high availability
❖
page 
Fig. 10.2.