Raid concepts – Avago Technologies 3ware SAS 9750-16i4e User Manual
Page 18
Chapter 1. Introduction to the 3ware Command Line Interface
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3ware SATA+SAS RAID Controller Card CLI Guide, Version 10.2
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“Available RAID Configurations” on page 11
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“Determining Which RAID Level to Use” on page 16
RAID Concepts
The following concepts are important to understand when working with a
RAID controller:
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Arrays and Units
. In the storage industry, an array refers to two or more
disk drives that appear to the operating system as a single unit. When
working with a RAID controller, unit refers to an array of disks that you
can configured and manage through the 3ware software. You can also use
the 3ware software to configure Single-disk units.
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Mirroring
. Mirrored arrays (RAID 1) write data to paired drives
simultaneously. If one drive fails, the data is preserved on the paired
drive. Mirroring provides data protection through redundancy. In
addition, mirroring using a 3ware RAID controller provides improved
performance because the 3ware TwinStor® technology reads from both
drives simultaneously.
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Striping
. Striping across disks allows data to be written and accessed on
more than one drive simultaneously. Striping combines each drive’s
capacity into one large volume. Striped disk arrays (RAID 0) achieve
highest transfer rates and performance at the expense of fault tolerance.
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Distributed Parity
. Parity works in combination with striping on RAID 5,
RAID 6, and RAID 50. Parity information is written to each of the striped
drives, in rotation. If a failure occurs, you can reconstructed the data on
the failed drive from the data on the other drives.
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Hot Swap
. The process of exchanging a drive without shutting down the
system. This process is useful when you need to exchange a defective
drive in a redundant unit.
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Array Roaming.
The process of removing a unit from a controller and
putting it back either on the same controller, or a different controller, and
having the unit recognized as a unit. You can attach the disks to different
ports without harm to the data.