DataDirect EF2800 Guía de usuario Pagina 211

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DataDirect Networks EF2800 FC RAID Storage System User Guide (V 1.0)
Array Basics
B.1.4 RAID 4
RAID 4 is similar to RAID 3 in that the redundant information is
achieved in the form of parity data. The user data is distributed across
all but one of the disks. The EF2800 uses a single, dedicated parity drive
for data protection. The main difference is that RAID 3 usually
synchronizes writes to its disks, while RAID 4 can send data to its disk
independently.
RAID 4 is best suited for transaction processing applications that
require high read requests, but not write requests such as inquires
rather than updates.
RAID 4 is not recommended for I/O-intensive applications that require
high data transfer rates.
B.1.5 RAID 5
RAID 5 arrays contain redundant information in the form of parity data,
which is calculated block-by-block for all user data. The parity
information is distributed across the disks in the array and occupies the
equivalent capacity of approximately one disk. Data is interspersed
with the parity information. If one disk in the array fails, the data on the
failed disk can be reconstructed from the parity data and user data on
the remaining disks. Two disks must fail before the entire array fails.
The read performance of a RAID 5 array is excellent, comparable to
that of a RAID 0 array. Write performance is lower than that of a RAID 0
array, because write operations involve calculating and writing new
parity data as well as writing the new user data.
B.1.6 RAID 50
RAID 50 arrays are made up of two or more RAID 5 arrays, across
which data is striped. RAID 50 arrays contain redundant information in
the form of parity data, which is calculated block-by-block for all user
data. As in a RAID 5 array, the parity information is distributed across
the disks in the array and occupies the equivalent capacity of one disk
per RAID 5. Data is interspersed with the parity information. If one disk
in the array fails, the data on the failed disk can be reconstructed from
the parity data and user data on the remaining disks. Two disks in one
RAID 5 subset must fail before the entire array fails.
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