Lesson 4: RAID- Redundant Array of Independent Disks

RAID

is a data storage virtualization technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both

RAID levels

Data is distributed across the drives in one of several ways, referred to as _______________, depending on the required level of redundancy and performanc

RAID

The different schemes, or data distribution layouts, are named by the word "____________" followed by a number, for example RAID 0 or RAID 1.

RAID system

A _____________ consists of two or more drives working in parallel. These can be hard discs, but there is a trend to also use the technology for SSD (Solid State Drives)

RAID 0 - Striping

RAID Levels

In a ___________ system data are split up into blocks that get written across all the drives in the array. By using multiple disks (at least 2) at the same time, this offers superior I/O performance.

RAID 0 - Striping

Advantages

__________ offers great performance, both in read and write operations. There is no overhead caused by parity controls.

RAID 0 - Striping

All storage capacity is used, there is no overhead.

RAID 0 - Striping

The technology is easy to implement.

RAID 0 - Striping

Disadvantages

__________is not fault tolerant. If one drive fails, all data in the _________ array are lost. It should not be used for mission-critical systems.

RAID 0 - Striping

Ideal use:

____________ is ideal for non-critical storage of data that have to be read/written at a high speed, such as on an image retouching or video editing station

RAID 0 - Striping

Ideal use:

If you want to use ______ purely to combine the storage capacity of twee drives in a single volume, consider mounting one drive in the folder path of the other drive. This is supported in Linux, OS X as well as Windows and has the advantage that a single drive failure has no impact on the data of the second disk or SSD drive.

RAID 1 - Mirroring

RAID Levels

Data are stored twice by writing them to both the data drive (or set of data drives) and a mirror drive (or set of drives). If a drive fails, the controller uses either the data drive or the mirror drive for data recovery and continuous operation. You need at least 2 drives for a RAID 1 array

RAID 1 - Mirroring

Advantages

__________ offers excellent read speed and a write speed that is comparable to that of a single drive.

RAID 1 - Mirroring

In case a drive fails, data do not have to be rebuild, they just have to be copied to the replacement drive.

RAID 1 - Mirroring

_________ is a very simple technology

RAID 1 - Mirroring

Disadvantages

The main disadvantage is that the effective storage capacity is only half of the total drive capacity because all data get written twice.

RAID 1 - Mirroring

Disadvantages

Software _________ solutions do not always allow a hot swap of a failed drive. That means the failed drive can only be replaced after powering down the computer it is attached to. For servers that are used simultaneously by many people, this may not be acceptable. Such systems typically use hardware controllers that do support hot swapping.

RAID 1 - Mirroring

Ideal use:

_________ is ideal for mission critical storage, for instance for accounting systems. It is also suitable for small servers in which only two data drives will be used.

RAID 5 - Striping with parity

RAID Levels

The most common secure RAID level. It requires at least 3 drives but can work with up to 16. Data blocks are striped across the drives and on one drive a parity checksum of all the block data is written. The parity data are not written to a fixed drive, they are spread across all drives

RAID 5 - Striping with parity

Advantages

Read data transactions are very fast while write data transactions are somewhat slower (due to the parity that has to be calculated).

RAID 5 - Striping with parity

Advantages

If a drive fails, you still have access to all data, even while the failed drive is being replaced and the storage controller rebuilds the data on the new drive.

RAID 5 - Striping with parity

Disadvantages

Drive failures have an effect on throughput, although this is still acceptable.

RAID 5 - Striping with parity

Disadvantages

This is complex technology. If one of the disks in an array using 4TB disks fails and is replaced, restoring the data (the rebuild time) may take a day or longer, depending on the load on the array and the speed of the controller. If another disk goes bad during that time, data are lost forever.

RAID 5 - Striping with parity

Ideal use:

__________ is a good all-round system that combines efficient storage with excellent security and decent performance. It is ideal for file and application servers that have a limited number of data drives.

RAID 6 - Striping with double parity

RAID Levels

_________ is like RAID 5, but the parity data are written to two drives. That means it requires at least 4 drives and can withstand 2 drives dying simultaneously.

RAID 6 - Striping with double parity

Advantages

Like with RAID 5, read data transactions are very fast.

RAID 6 - Striping with double parity

Advantages

If two drives fail, you still have access to all data, even while the failed drives are being replaced. So _________ is more secure than RAID 5.

RAID 6 - Striping with double parity

Disadvantages

Write data transactions are slower than RAID 5 due to the additional parity data that have to be calculated. In one report I read the write performance was 20% lower.

RAID 6 - Striping with double parity

Disadvantages

Drive failures have an effect on throughput, although this is still acceptable again.

RAID 6 - Striping with double parity

Disadvantages

This is complex technology. Rebuilding an array in which one drive failed can take a long time.

RAID 6 - Striping with double parity

Ideal use:

________ is a good all-round system that combines efficient storage with excellent security and decent performance. It is preferable over RAID 5 in file and application servers that use many large drives for data storage.

RAID level 10 - combining RAID 1 & RAID 0

RAID Levels

This is a nested or hybrid RAID configuration. It provides security by mirroring all data on secondary drives while using striping across each set of drives to speed up data transfers.

RAID 0 and RAID 1

RAID Levels

It is possible to combine the advantages (and disadvantages) of ___________ in one single system.

RAID level 10 - combining RAID 1 & RAID 0

This is a nested or hybrid RAID configuration.

RAID level 10 - combining RAID 1 & RAID 0

It provides security by mirroring all data on secondary drives while using striping across each set of drives to speed up data transfers.

RAID level 10 - combining RAID 1 & RAID 0

Advantages

If something goes wrong with one of the disks in a __________ configuration, the rebuild time is very fast since all that is needed is copying all the data from the surviving mirror to a new drive. This can take as little as 30 minutes for drives of 1 TB.

RAID level 10 - combining RAID 1 & RAID 0

Disadvantages

Half of the storage capacity goes to mirroring, so compared to large RAID 5 or RAID 6 arrays, this is an expensive way to have redundancy.

RAID levels 2, 3, 4 and 7

These levels do exist but are not that common (RAID 4 is essentially like RAID 5 but with the parity data always written to the same drive).

Hardware-based/ Hardware RAID

Types of RAID

________setup, the drives connect to a special RAID controller inserted in a fast PCI-Express (PCI-e) slot in a motherboard

Hardware-based/ Hardware RAID

Types of RAID

_________ controllers can be configured through card BIOS before an operating system is booted, and after the operating system is booted, proprietary configuration utilities are available from the manufacturer of each controller.

Hardware-based/ Hardware RAID

Types of RAID

Advantages:

• ________ is dedicated processing system, using controllers or RAID cards to manage the RAID configuration independently from the operating system. The RAID controller does not take processing power away from the disks it manages. Thus, more space and speed can be used to read and write data. It can work on any operating system. Replacing failed disk is simple - Just plug it out and put in a new one.

Hardware-based/ Hardware RAID

Types of RAID

Disadvantages:

• As __________requires additional controller hardware, the cost is higher than software RAID. If your RAID controller fails, you have to find a compatible one to replace in order to get the RAID system to perform the way you set it up.

Software-based/ Software RAID

Types of RAID

When storage drives are connected directly to the motherboard without a RAID controller, RAID configuration is managed by utility software in the operating system, and thus referred to as a software RAID setup

Software-based/ Software RAID

Types of RAID

___________ implementations are provided by many modern operating systems.

Software-based/ Software RAID

Types of RAID

Advantages:

• Unlike hardware RAID, __________ uses the processing power of the operating system in which the RAID disks are installed. The cost is lower because no additional hardware RAID controller is required. It also permits user

Software-based/ Software RAID

Types of RAID

Disadvantages:

• _________ tends to be slower than hardware RAID. Since some processing power is taken by the software, read and write speeds of your RAID configuration, along with other operations carried out on the server can be slowed down by it. ____________ is often specific to the operating system being used, so it cannot generally be used for partitions that are shared between operating systems.

Software-based/ Software RAID

Types of RAID

Disadvantages:

• Replacing failed disk in the __________ is a bit more complex. You have to firstly tell your system to stop using the disk and then replace the disk.

back-ups

RAID is no substitute for _________

RAID 0

All RAID levels except _________ offer protection from a single drive failure. A RAID 6 system even survives 2 disks dying simultaneously. For complete security, you do still need to back-up the data stored on a RAID system.

power spike

• That back-up will come in handy if all drives fail simultaneously because of a _________.

stolen

• It is a safeguard when the storage system gets ________

natural disaster or fire

• Back-ups can be kept off-site at a different location. This can come in handy if a ______________ destroys your workplace.

user error

• The most important reason to back-up multiple generations of data is _________. If someone accidentally deletes some important data and this goes unnoticed for several hours, days, or weeks, a good set of back-ups ensure you can still retrieve those files