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What is RAID and how can it work best for me?

What is RAID and how can it work best for me?
Use RAID to increase the performance and reliability of your data storage

Redundant Array of Independent (or Inexpensive, depending on who you ask) Disks (RAID) is a technology employed by many companies to increase the performance and reliability of their data storage.

The RAID system basically takes 2 or more hard disk drives (HDD) and gets them to work in parallel. RAID systems can be configured to meet the needs of your business with these goals in mind.

  • Performance
  • Reliability/resilience
  • Storage capacity

To achieve this RAID uses "schemes" or, to be more precise, RAID levels, with each RAID level providing a different balance of these three goals. It's worth mentioning that there is a minimum number of disks required to use each RAID Level.

RAID approaches

There are two possible RAID approaches: Hardware RAID and Software RAID.

Hardware RAID

Hardware RAID

A hardware RAID employs the use of specialised hardware called a RAID controller which connects to and manages the hard disk drives. The RAID controller can be on a separate card that connects to the computer or it can be included on the computer's motherboard. The hardware RAID offers better performance but tends to cost more than the software alternative.

Software RAID
Software RAID

A software RAID does not require the use of specialised hardware. Many operating systems include Software RAID functionality as standard, such as Windows Server (2003 and above), MAC OS X and Linux.

RAID levels

To give you a better idea of the RAID levels concept I will describe the most popular RAID levels along with their minimum requirements and the pros and cons of each.

Level: RAID 0
AKA: Striping
Best for: Performance and capacity
Minimum no. of disks required: 2

RAID 0

In a RAID Level 0 scheme, data files are spread across all participating hard disk drive (HDDs). This level offers superior performance as this allows the system to split the data, allowing it to read and write across multiple HDDs simultaneously.

Advantages

  • Good read and write performance
  • Simple to setup
  • Allows all of the disks storage capacity to be used, e.g. if you are have two 1TB drives in a RAID 0 scheme the system will combine those two drives so that you store 2TB worth of data

Disadvantages

  • RAID 0 does not provide any fault tolerance. If a single disk fails within this type of scheme then all the data is lost, so make sure you have a back up

When to consider this option

If the data is non-critical, performance is key and downtime isn't a concern RAID 0 is a strong candidate. This scheme paired with a backup solution can work well in situations such as image editing, video editing and gaming.

Level: RAID 1
AKA: Mirroring
Best for: Reliability and resilience
Minimum no. of disks required: 2

RAID 1
In a RAID Level 1 scheme the same data is written to more than one hard disk drive. This level offers increased resilience; in the case of a single HDD failure the data can still be accessed from the mirror HDD or set.

Advantages

  • Resilience and reliability. In the case of a single HDD drive failure the data will still be available to the operating system. This gives the administrator time to replace the failed HDD without losing data
  • Has comparable read and write speed to that of a single HDD
  • Simple to setup

Disadvantages

  • As the RAID 1 scheme mirrors the data onto another HDD or set of disks, only half of the total storage space is available to the operating system.

When to consider this option

If the data is critical and reliability is paramount RAID 1 is a strong candidate. This scheme paired with a backup solution can work well to provide high uptime. This scheme can be recommended for small servers with two disks.

Level: RAID 5
AKA: Striping with Parity
Best for: Reliability, performance and capacity
Minimum no. of disks required: 3
RAID 5

In a RAID Level 5 the data is distributed across all the hard disk drives. This increases performance while providing a level of redundancy. When data is written to the disk the RAID 5 reserves some space for parity information, which allows the RAID 5 to recover lost data.

The parity information is also distributed across all the HDDs, and enables the data to be recovered if any single disk in the RAID 5 scheme fails.
Although the RAID 5 scheme offers redundancy, it cannot tolerate multiple disk failures so it is advisable to take regular backups.

Advantages

  • Increased read performance
  • Will tolerate a single disk failure
  • Automatically uses data from the remaining disks to reconstruct the data from the failed disk

Disadvantages

  • Write speeds may be slightly slower than RAID 1 as the parity information (used to recover data in the event of a failure) has to be calculated
  • Although it will tolerate a single disk failure it will operate at reduced performance until the broken disk is replaced
  • The equivalent of one disk will be used to store the parity information
  • A more complex solution

When to consider this option

RAID 5 can be considered a good all-rounder and is often used with file and application servers.

Level: RAID 1+0 (10)
AKA. A stripe of mirrors
Best for: Performance & reliability
Minimum no. of disks required: Traditionally 4

Mirrored Disks

A RAID Level 10 scheme is technically a combination of RAID Level 1 + RAID Level 0; mirroring and striping, without parity.

Put simply the data is striped much like a RAID 0. The difference is that each member of the striped set has its data mirrored to another disk. This RAID level can also tolerate multiple disk failures if one disk fails in each mirrored set.

Advantages

  • Performance will be similar to that of RAID 1
  • Will tolerate multiple disk failures
  • Automatically uses the data from the remaining disks to reconstruct data from a failed disk

Disadvantages

  • Like RAID 1, due to the data being mirrored only half of the total space is usable
  • Can still suffer data loss if all disks in a mirrored set fail
  • More complex
  • Expensive to maintain, as disks need to be added in pairs

When to consider

RAID 10 is a good idea for critical databases and servers especially when uptime and performance is key. It is often preferred over RAID 5 as the performance degradation is not as severe when a single drive fails. This is because the data from the mirror will be used. With RAID 5 the data from the remaining drives needs to be read, and the missing data calculated using the parity information.

There are many other RAID level schemes not mentioned in this article such as RAID 3, RAID 6 and JBOD (Just a Bunch of Disks/Drives.) Each have their own distinct advantages and disadvantages.

I have decided on a Raid level. What next?

We incorporate RAID level schemes in both our server configurations and our Network Attached Storage (NAS) solutions.

Each of our clients requires a different balance between performance, reliability and affordability, and so we will run through the pros and cons of each option, taking into consideration the client's requirements. We then make a recommendation, and leave the final choice up to the client.

I hope this short guide has helped you distinguish between some of the more popular RAID Levels. If you are still unsure as to which RAID solution would be good for you and your business, please give us a call on 0114 299 4050.

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