Configuring your Storage
Choosing a RAID Array Level
Cisco Small Business NSS3000 Series Network Storage System Administration Guide
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Choosing a RAID Array Level
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 technically not a RAID level.
These variables are used in the formulas used to calculate the total capacity of
each RAID level:
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m: capacity of the smallest disk in the array
•
n: number of disks in the array
Stripe (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 * 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.
Mirror (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 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
