Dell Servers - What are the RAID levels and their specifications?

Dell Servers - What are the RAID levels and their specifications?


RAID is a data storage virtualization technology that combines multiple physical disk drive components into a single logical unit for the purposes of data redundancy, performance improvement, or both.


Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the required level of redundancy and performance. The different schemas, or data distribution layouts, are named by the word RAID followed by a number, for example RAID 0 or RAID 1. Each schema, or RAID level, provides a different balance among the key goals:
reliability, availability, performance, and capacity.

RAID levels greater than RAID 0 provide protection against unrecoverable sector read errors, as well as against failures of whole physical drives.

Warning: The RAID technology is not a backup solution. It does not replace a good data backup solution for data retention and security.

Table of Content:

  1. RAID Levels
  2. RAID Terminology
  3. Videos

1. RAID Levels

Level

Striping

Mirroring

Parity

Disk Failure
Tolerance

Minimum
disks

Details

RAID 0

X

0

2

RAID 1

X

1

2

RAID 5

X

X

1

3

RAID 6

X

X

2

4

RAID 5 + Additional parity block

RAID 10

X

X

1 per mirror set

4

RAID 0 + RAID 1

RAID 50

X

X

6

RAID 0 + RAID 5

RAID 60

X

X

8

RAID 0 + RAID 6


2. RAID Terminology

Allows you to write data across multiple physical disks instead of just one physical disk. RAID 0 involves partitioning each physical disk storage space into 64 KB stripes. These stripes are interleaved in a repeated sequential manner. The part of the stripe on a single physical disk is called a stripe element.
For example, in a four-disk system using only RAID 0, segment 1 is written to disk 1, segment 2 is written to disk 2, and so on. RAID 0 enhances performance because multiple physical disks are accessed simultaneously, but it does not provide data redundancy (Figure 1 (English only)).

Disk1

Figure 1: RAID 0

  • Fault Tolerance – None
  • Advantage – Improved performance, Additional storage
  • Disadvantage – Should not be used for critical data Data Loss will occur with any drive failure.

With RAID 1, data written to one disk is simultaneously written to another disk. If one disk fails, the contents of the other disk can be used to run the system and rebuild the failed physical disk.
The primary advantage of RAID 1 is that it provides 100 percent data redundancy. Because the contents of the disk are completely written to a second disk, the system can sustain the failure of one disk. Both disks contain the same data at all times. Either physical disk can act as the operational physical disk (Figure 2 (English only)).

Note: Mirrored physical disks improve read performance by read load balance.

Disk2

Figure 2: RAID 1

  • Fault Tolerance – Disk errors, Single disk failure
  • Advantage – High read performance, Fast recovery after drive failure, Data redundancy
  • Disadvantage – High disk overhead, Limited capacity
RAID 5 and 6: Parity Data is redundant data that is generated to provide fault tolerance within certain RAID levels. In the event of a drive failure the parity data can be used by the controller to regenerate user data.
Parity data is present for RAID 5, 6, 50, and 60. The parity data is distributed across all the physical disks in the system. If a single physical disk fails, it can be rebuilt from the parity and the data on the remaining physical disks.
  • RAID level 5 combines distributed parity with disk striping, as shown below (Figure 3 (English only)). Parity provides redundancy for one physical disk failure without duplicating the contents of entire physical disks.
  • RAID 6 combines dual distributed parity with disk striping (Figure 4 (English only)). This level of parity allows for two disk failures without duplicating the contents of entire physical disks.

RAID 5
DISK3

Figure 3: RAID 5

  • Fault Tolerance – Disk errors, Single disk failures
  • Advantage – Efficient use of drive capacity, High read performance, Med-to-High write performance
  • Disadvantage – Disk failure medium impact, Longer re-build due to parity re-calculation

RAID 6
Disk4

Figure 4: RAID 6

  • Fault Tolerance – Disk errors, Dual disk failures
  • Advantage – Data redundancy, High read performance
  • Disadvantage – Write performance decrease due to dual parity calculations, Extra cost due to 2 disk equivalent devoted to parity
RAID 10: RAID 10 requires two or more mirrored sets working together. Multiple RAID 1 sets are combined to form a single array. Data is striped across all mirrored drives.
Since each drive is mirrored in RAID 10, no delay is encountered because no parity calculation is done.
This RAID strategy can tolerate the loss of multiple drives as long as two drives of the same mirrored pair do not fail. RAID 10 volumes provide high data throughput and complete data redundancy (Figure 5 (English only)).
DISK5

Figure 5: RAID 10

  • Fault Tolerance – Disk errors, One disk failure per mirrored set
  • Advantage – High read performance, Supports largest RAID group of 192 drives
  • Disadvantage – Most expensive



3. Videos

a. Introduction to RAID Concepts

b. Understanding RAID Levels

c. Understanding Parity

d. Understanding Strip Size, Stripe Width and Stripe Size



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Article ID: SLN292050

Last Date Modified: 02/28/2018 12:10 PM


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