RAID and RAID Controllers

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What is RAID and Why do Your Customers Need it?
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RAID and RAID Controllers
RAID (Redundant Array of Inexpensive Disks) is a data storage structure that allows a data
center to combine two or more physical storage devices (HDDs, SSDs, or both) into a logical
unit that is seen by the attached system as a single drive.
There are two basic RAID configurations:
What is a Controller Card?
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A controller card is a device that sits between the host system and the storage system, and
allows the two systems to communicate with each other.
1. Striping (RAID 0) writes some data to one drive and some data to another,
minimizing read and write access times and improving I/O performance.
2. Mirroring (RAID 1) copies all information from one drive directly to another, preventing loss of data in the event of a drive failure.
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Mirroring
Mirroring & Striping
Duplicates data from primary
drive to secondary drive
Mirrors data that is striped,DRIVE
spread
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evenly across multiple disks
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There are two types of controller cards: Host Bus Adapters (HBAs), and RAID controller cards.
1.
An HBA is an expansion card that plugs into a slot (such as PCI-e) on the computer
system’s motherboard and provides fast, reliable non-RAID I/O between the host and
the storage devices. HBAs can reliably connect hundreds or even thousands of hard
disk drives (HDDs), tape, and solid state drives (SSDs) to the host, making them ideal
for cost-sensitive tape backup solutions or high-performance SSD environments.
2.
A RAID controller card is similar to an HBA, but can also add redundancy (RAID),
optimize performance, reduce latency, or even make smart decisions on whether to store
data on an HDD or an SSD cache, depending on user needs. Since these additional
tasks consume power and processing speed, RAID controllers are typically more
expensive than HBAs and handle fewer devices.
Controller
Features
HBA
Low cost, high connectivity, limited functionality,
best performance
RAID
Intelligent data management, redundant logical configuration
support, broadest functionality, optimized performance,
cache backup
HBAs vs. RAID Controllers
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RAID can be hardware-based or software-based.
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Hardware RAID resides on a PCI-X or PCIe controller card, or on a motherboard-integrated
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RAID-on-Chip (ROC).
• Primary benefit: Offloads RAID tasks from the host system, yielding better performance
than software RAID. Controller cards can be easily swapped out for replacement and
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upgrades. Data can be backed upDRIVE
to 1prevent loss in a power failure.
• Primary drawback: More expensive
software RAID.
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Software RAID runs entirely on the CPU of the host computer system.
• Primary benefit: Lower cost due to lack of RAID-dedicated hardware.
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• Primary drawback: Lower RAID performance as CPU also powers the operating system
and applications. No data backup. DRIVE 2
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Levels of RAID
Glossary
Benefit
Connector: A plug or socket that links
devices together.
Spreads data evenly over multiple drives to
enhance performance. Because there is no redundancy scheme, it does not provide data protection.
Highest performance
Copyback Hot Spare: When a failed drive is
replaced, data is automatically copied from
the hot spare back to the replaced drive.
RAID 1
Provides data protection by duplicating all data
from a primary drive onto a secondary drive.
Highest data protection
RAID 1E
Combines data striping from RAID 0 with data
mirroring from RAID 1 to extend RAID 1 data
availability across an odd number of disks.
Highest data protection
for an odd number of
disks
Combines data striping (for enhanced performance) with distributed parity (for data protection)
to provide a recovery path in case of failure.
Best cost/performance
balance for multi-drive
environments
Data striping with distributed parity with hotspare
integrated into the array.
The cost/performance
balance of RAID 5
without setting aside a
dedicated hotspare disk
RAID
Level
Description
RAID 0
RAID 5
RAID 5EE
RAID 6
Provides double redundancy and the ability to
sustain two drive failures. Data is striped across
at least 4 physical drives. A second parity scheme
is used to store and recover data.
Highest fault tolerance
with the ability to survive
two disk failures
RAID 10
Combines RAID 0 (data striping) and RAID 1
(disk mirroring).
Highest performance with
highest data protection
RAID 50
Combines multiple RAID 5 sets with data striping
(RAID 0) to increase capacity and performance
without adding disks to each RAID 5 array.
Increased capacity
and performance for
multi-array RAID 5
environments
RAID 60
Combines multiple RAID 6 sets with data striping
(RAID 0) to increase capacity and performance
without adding disks to each RAID 6 array.
Highest fault tolerance
with the highest data
protection
Dual Drive Failure Protection (RAID 6,
60): Provides double redundancy and the
ability to sustain two drive failures. Data
is striped across at least 4 physical drives.
A second parity scheme is used to store
and recover data.
Fault Tolerance: The ability of a system
to continue to perform its functions even
when one or more of its hard disk drives
have failed.
Hard Disk Drive (HDD): A motorized mechanical device that stores data on rotating
magnetic platters. HDDs are typically
slower than flash memory.
Host Bus Adapter (HBA): A hardware
component that connects the computer
(the host) to storage devices.
Hot Space (RAID 5EE): Provides the protection of RAID 5 and adds a hot spare disk
to the array. This extra drive enhances RAID
5 performance with higher IOPs.
Hot Spare: A spare hard drive which will
automatically be used to replace a failed
member of a redundant disk array.
Hot Swap: The ability to replace a failed
member of a redundant disk array without
bringing down the server or interrupting
transactions that involve the other devices.
IOPs: Input/Output operations per second.
Mirroring (RAID 1): Provides data protection by duplicating all data from a primary
drive onto a secondary drive.
Parity: A form of data protection used by
RAID 5 to re-create the data of a failed drive.
Port: The outlet on the RAID controller that
connects the controller to the disk drive.
Port expander: Hardware that allows multiple disk drives to be connected to a single
RAID controller port.
SAS: Serial Attached SCSI (see SCSI
below). The latest generation of the SCSI
interface, it combines the reliability and
stability of SCSI with higher performance
and scalability, making it more expensive
than SATA options.
SATA: Serial ATA. The most common interface for disk drives, SATA offers significantly
higher transfer speeds than parallel ATA
(PATA). SATA storage is low cost and high
capacity.
SCSI: (Pronounced “scuzzy”). Small Computer System Interface. SCSI is the industry standard interface for connecting and
transferring data between computers and
peripheral devices, including disk drives.
Solid State Drive (SSD): A data storage
device that uses non-moving flash memory
instead of the rotating platters of a hard
disk drive to store data. SSDs typically
outperform HDDs.
I/O: Input/Output. The transfer of data to
or from a computer and to or from a peripheral device, such as HDD and SDDs. Every
transfer is an output from one device and
an input into another.
Figure 4. RAID Levels
For more information:
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