LaCie Biggest Quadra | Understanding RAID |
User Manual | page 18 |
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3.3. RAID 5
Independent Data Disks With Distributed Parity Blocks
This is the most versatile RAID level and offers high I/O transaction rates, which greatly helps applications that perform large numbers of concurrent requests. If one drive in a RAID 5 array fails, the lost data can be rebuilt from data on the remaining, functional disks.
Essentially, RAID level 5 is a striped set with parity, and requires at least three disks to implement. In this configuration, data is saved across several hard disks, as in a RAID 0 array, but parity information is also saved across the disks. It is this parity information which pro- vides the
Storage capacity in a RAID level 5 configuration is the result of a mathematical expression that compares
■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
This diagram represents a
ERAID 5 array, consisting of
D | four disks, which are | |
C | connected to the Controller. | |
Parity blocks are represented | ||
B | ||
by the letter P. | ||
A |
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CONTROLLER
data from the drives and a calculates another piece of data called parity. In this situation, then, storage capacity is calculated by multiplying the number of disks in the array, minus one, by the capacity of the smallest disk in the array. So, for instance, if a RAID 5 array is created with four drives of varying capacities of 40GB, 50GB, 60GB and 70GB, the total capacity of the array would be 120GB [3 (4 disks – 1 disk) x 40 = 120].
■Recommended Uses
❖File and Application Servers
❖Database Servers
❖Web,
❖Intranet Servers
A D G
PJKL
B
E
PGHI
J
C
PDEF
H
K
PABC
F
I
L
Fig. 3.3.