LaCie Two Big eSATA & USB
User Manual
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7.2. Safe (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.
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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C
D
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B
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G
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CONTROLLER
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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.
Fig. 7.2.A.
Recommended Uses
Payroll
Accounting
Financial
Any use that requires high availability
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Understanding RAID and Storage Policies
