Choosing A Raid Array Level - Linksys NSS6000 Series Administrator's Manual

Configuring your Storage

Choosing a RAID Array Level

Choosing a RAID Array Level
Linksys Small Business NSS4000 and NSS6000 Series Network Storage System Administration Guide
RAID (Redundant Array of Inexpensive Disks) is a technology that enables multiple
low-cost hard drives to be used together in a way that increases performance
and/or reliability compared to that of a single drive. The component devices in a
RAID array appear as a single logical storage device. There are various types of
RAID, referred to as RAID levels. Some RAID levels increase the performance of
the array, some increase the reliability, and others do a mixture of both. The NSS
supports the following RAID levels: 0, 1, 5 and 10. The NSS also supports JBOD
(Just a Bunch of Disks), which is not technically a RAID level.
These variables are used in formulas used to calculate the total capacity of each
RAID level:
•
m – capacity of the smallest disk in the array
•
n – number of disks in the array
RAID0: RAID0 stripes the data written to the array across the component disks.
The data is broken into chunks and each chunk is written to a different disk. Reads
and writes to each disk occur in parallel, speeding up the total read and write
performance of the array.
•
Minimum Number of Disks: 2
•
Total capacity: m x n
•
Advantages: Increased read and write performance.
•
Disadvantages: Decreased reliability. A failure of any component disk in the
array causes the entire array to fail.
RAID1: RAID1 writes the same data to each disk in the array. The disks are referred
to as "mirrors" because each one mirrors the data stored on the others. As long as
one disk in the array is intact, all data can be read back from the array. If a disk fails
in the array and is then replaced, the array must copy the entire contents of a good
disk to the new disk. This process is referred to as "resyncing." During a resync,
the array continues to be available for reads and writes. When an array contains a
failed disk, it is said to be operating in degraded mode. This reflects the
decreased performance and reliability of the array when it is missing disks.
•
Minimum Number of Disks: 2
•
Total capacity: m
•
Advantages: Increased reliability. The array can sustain the loss of all but
one disk without any data loss. Each mirror disk added to the array
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