RAID Systems

RAID meaning

Redundant Array of Independent Disks

RAID purpose

Combine multiple physical disk drives into one logical unit to provide protection performance or both

Why RAID improves performance

It can serve IOs from multiple drives simultaneously

Striping definition

Splits data into equal sized blocks and writes them across multiple disks to increase speed

Striping commonly used in

RAID 0 RAID 5 RAID 6 and RAID 10

Striping advantage

Improved read and write performance because multiple disks work together

Striping disadvantage in RAID 0

No fault tolerance because there is no redundancy so one disk failure loses all data

Mirroring definition

Duplicates the same data across two or more disks for fault tolerance

Mirroring used in

RAID 1 and RAID 10

Mirroring advantages

High fault tolerance fast recovery and improved read performance

Mirroring disadvantages

High cost and only about half of total disk space is usable for data

Parity definition

Extra information stored to rebuild lost data if a disk fails without full duplication

Parity used in

RAID 4 RAID 5 and RAID 6

How parity is calculated

Parity block is generated using XOR on the data blocks

Parity advantage

Provides redundancy and is more storage efficient than mirroring

Parity disadvantage

Slower write performance due to parity calculation and extra writes

RAID 0 name

Striping

RAID 0 how it works

Data is striped across multiple disks so reads and writes run in parallel

RAID 0 minimum drives

2

RAID 0 objective

Improve performance data read and write speed

RAID 0 advantage

Enhanced performance

RAID 0 challenge

No data redundancy

RAID 0 usable capacity

100 percent of all drives

RAID 0 fault tolerance

0 any drive failure causes data loss

RAID 1 name

Mirroring

RAID 1 how it works

Data is duplicated on two or more drives so each holds an identical copy

RAID 1 typical number of drives

Most often implemented with 2 drives

RAID 1 objective

Data redundancy and improved read performance

RAID 1 advantages

High data redundancy and improved read performance

RAID 1 challenges

Reduced usable capacity and increased cost due to duplication

RAID 1 usable capacity

About 50 percent because half storage is used for mirroring

RAID 1 fault tolerance

1 drive per mirrored pair

RAID 4 name

Block level striping with dedicated parity

RAID 4 how it works

Data is striped across disks and parity is stored on one dedicated parity disk

RAID 4 advantage

If a disk fails missing data can be rebuilt using the parity disk

RAID 4 challenge

Parity disk becomes a write bottleneck because all writes must update it

RAID 4 minimum drives

3

RAID 5 name

Distributed parity

RAID 5 how it works

Data is divided across all disks and parity is distributed between disks

RAID 5 minimum drives

3

RAID 5 key improvement over RAID 4

No single parity bottleneck because parity is spread across disks

RAID 5 advantages

Better load balancing and faster writes than RAID 4 with balanced performance and reliability

RAID 5 fault tolerance

1 drive can fail and the system can rebuild using parity

RAID 5 usable capacity

N minus 1 drives worth of capacity

RAID 10 name

Mirrored stripes

RAID 10 how it works

Combines RAID 0 and RAID 1 by striping across mirrored pairs of drives

RAID 10 minimum drives

4

RAID 10 objective

Performance improvement and high data redundancy

RAID 10 advantages

Excellent data redundancy and excellent read and write performance

RAID 10 challenge

Higher cost because more drives are required

RAID 10 usable capacity

About 50 percent because half storage is used for mirroring

RAID 10 fault tolerance

Multiple drives can fail as long as no mirrored pair loses both drives

RAID 5 best use

Balanced performance and reliability

RAID 10 best use

Databases virtualization and enterprise applications

RAID 0 best use

High speed workloads such as video editing

RAID 1 best use

Critical small storage such as OS or a home server

RAID 4 best use

Legacy systems and rare today