Avago Technologies 3ware SAS 9750-4i - Manual (Page 16)

Chapter 1. Introduction to the 3ware Command Line Interface
8 3ware SATA+SAS RAID Controller Card CLI Guide, Version 10.0
• In commands, brackets around an item indicates that it is optional.
• In commands, ellipses (...) indicate that more than one parameter at a time
can be included, for example, /c0/p0 show attribute [attribute ...], or that
there is a range between two values from which you can pick a value, for
example, /cx set carvesize=[1024...2048].
• In commands, a vertical bar (|) indicates an 'or' situation where the user
has a choice between more than one attribute, but only one can be
specified.
Example: In the command to rescan all ports and reconstitute all units, the
syntax appears as /cx rescan [noscan]. The brackets [ ] indicate that you may
omit the noscan parameter, so that the operation will be reported to the
operating system.
Understanding RAID Levels and Concepts
3ware RAID controllers use RAID (Redundant Array of Independent Disks)
to increase your storage system’s performance and provide fault tolerance
(protection against data loss).
This section organizes information about RAID concepts and configuration
levels into the following topics:
• “RAID Concepts” on page 8
• “Available RAID Configurations” on page 9
• “Determining What RAID Level to Use” on page 15
RAID Concepts
The following concepts are important to understand when working with a
RAID controller:
• Arrays and Units . In the storage industry, the term “array” is used to
describe two or more disk drives that appear to the operating system as a
single unit. When working with a 3ware RAID controller, “unit” is the
term used to refer to an array of disks that is configured and managed
through the 3ware software. Single-disk units can also be configured in
the 3ware software.
• 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 3ware’s TwinStor® technology reads from both
drives simultaneously.