LaCie 4BIG QUADRA USB 3.0 Guide de référence rapide

RAID Technology White Paper

As specialists in data storage, LaCie recognizes that almost all computer users will need a storage or backup solution and that

people use and store data in different ways. Depending on their requirements, some people may prioritize performance and ca-

pacity, whereas others may be more interested in security and speed. In order to meet the storage needs of a wide range of users,

LaCie’s professional storage devices utilize RAID technology.

RAID (Redundant Array of Independents Disks) is a simple technology that improves the performance of external storage so-

lutions. RAID allows you to choose the best way to use your device to ﬁt your needs. Simply put, RAID technology either divides or

duplicates the task of one hard disk between many (or as few as two) disks to either improve performance or create data redundancy

in case of a drive failure. You can decide how the device handles data by setting its RAID mode.

This document describes the different RAID levels used in LaCie professional storage devices, and the characteristics used by each

mode to optimize the speed, security or storage capacity of the hard drives in the RAID array.

RAID Terms

To better understand how RAID works, ﬁrst familiarize yourself with the terms below:

Striping✦is the splitting of data between multiple drives. Striped RAID arrays generally aim to merge maximum capacity

into one single volume.

Mirroring✦is the copying of data to more than one disk. Mirrored RAID arrays typically allow the failure of at least one disk

in the array without any data loss, depending on the RAID level of the array.

Fault Tolerance✦allows a RAID array to continue working (i.e. the data stored in the array is still available to the user) in

the event of a disk failure. Not all mirrored RAID arrays are user friendly. For instance, some RAID devices must be shut

down before a failed disk is replaced, whereas LaCie RAID devices feature “hot-swappaple” disk replacement that allows

the device to remain on, and the data accessible, while the failed disk is replaced.

Important:

No RAID conﬁguration will protect data reliability from software or ﬁle system corruption. As a result, LaCie recommends that

regular backups should always be performed to protect data.

Page 2

LaCie RAID Technology White Paper

STANDARD RAID LEVELS

RAID 0

RAID 0 (also called FAST mode in some LaCie devices), is the fastest RAID mode. Requiring at least 2 drives,

RAID 0 stripes data onto each disk. The available capacities of each disk are added together so that one logical

volume mounts on the computer.

If one physical disk in the array fails, the data of all disks becomes inaccessible because parts of the data have

been written to all disks.

RAID 0

Disk 1 Disk 2 Disk 3 Disk 4

Applications

RAID 0 is ideal for users who need maximum

speed and capacity. Video editors working with

very large ﬁles may use RAID 0 when editing mul-

tiple streams of video for optimal playback perfor-

mance. A RAID 0 array is more suited for actively

working with ﬁles (editing video, for example) and

should not be used as a single storage backup

solution or on mission critical systems.

LaCie Products with RAID 0

LaCie 2big quadra✦

LaCie 4big quadra✦

LaCie big disk quadra (built-in)✦

LaCie little big disk quadra (built-in)✦

LaCie 5big network✦

How RAID 0 Capacity Is Calculated

Each disk in a RAID 0 system should have the

same capacity.

Storage capacity in a RAID level 0 conﬁguration

is calculated by multiplying the number of drives

by the disk capacity, or C = n*d, where:

C = available capacity

n = number of disks

d = disk capacity

For example, in a RAID 0 array with four drives

each with a capacity of 1000GB, the total ca-

pacity of the array would be 4000GB:

C = (4*1000)

RAID 0

RAID 1

RAID 3

RAID 3+Spare

RAID 5

RAID 5+Spare

RAID 6

RAID 0+1

RAID 10

Concatenation

JBOD

RAID Selection

Page 3

LaCie RAID Technology White Paper

RAID 1

RAID 1 (also called SAFE mode in some LaCie devices) is a secure RAID mode that requires at least 2 drives

and works with pairs of drives. One logical volume mounts on the computer and the combined available

capacity of both drives is limited to the capacity of the lowest-capacity disk. If one physical disk fails, the data

is available immediately on the second disk. No data is lost if one disk fails.

Applications

RAID 1 provides maximum data safety in the

event of a single disk failure, but because data

is written twice, performance is reduced slight-

ly when writing. RAID 1 is a good choice when

safety is more important than speed.

LaCie Products with RAID 1

LaCie 2big quadra✦

LaCie 2big network✦

RAID 1

How RAID 1 Capacity Is Calculated

Each disk in a RAID 1 system should have the

same capacity.

Storage capacity in a RAID level 1 conﬁguration

is calculated by multiplying the number of drives

by the disk capacity and dividing by 2, or

C = n*d/2

where:

C = available capacity

n = number of disks

d = disk capacity

For example, in a RAID 1 array with four drives

each with a capacity of 1000GB, the total ca-

pacity of the array would be 2000GB:

C = (4*1000)/2

RAID 0

RAID 1

RAID 3

RAID 3+Spare

RAID 5

RAID 5+Spare

RAID 6

RAID 0+1

RAID 10

Concatenation

JBOD

RAID Selection

Page 4

LaCie RAID Technology White Paper

RAID 3

RAID 3 uses byte-level striping with a dedicated parity disk (Disk 4 in the illustrations, right) so that one volume

mounts on the computer. A RAID 3 array can tolerate a single disk failure without data loss. If one physical disk

fails, the data from the failed disk can be rebuilt onto a replacement disk. If a second disk fails before data can

be rebuilt to a replacement drive, all data in the array will be lost.

Applications

RAID 3 provides good data safety for environ-

ments where long, sequential ﬁles are being

read, such as video ﬁles. Disk failure does not

result in a service interruption because data is

read from parity blocks. RAID 3 is useful for

people who need performance and constant

access to their data, like video editors. RAID

3 is not recommended for intensive use with

nonsequential ﬁles because random read per-

formance is hampered by the dedicated parity

disk.

Ap(1-3)

Ap(4-6)

Bp(1-3)

Bp(4-6)

Cp(1-3)

Cp(4-6)

RAID 3

Disk 1 Disk 2 Disk 3 Disk 4

LaCie Products with RAID 3

LaCie 4big quadra✦

How RAID 3 Capacity Is Calculated

Each disk in a RAID 3 system should have the

same capacity.

Storage capacity in a RAID level 3 conﬁgura-

tion is calculated by subtracting the number

of drives by one and multiplying by the disk

capacity, or

C = (n-1)*d

where:

C = available capacity

n = number of disks

d = disk capacity

For example, in a RAID 3 array with four drives

each with a capacity of 1000GB, the total ca-

pacity of the array would be 3000GB:

C = (4-1)*1000

RAID 0

RAID 1

RAID 3

RAID 3+Spare

RAID 5

RAID 5+Spare

RAID 6

RAID 0+1

RAID 10

Concatenation

JBOD

RAID Selection

Page 5

LaCie RAID Technology White Paper

RAID 3+Spare

In RAID 3+Spare, one disk in the array is left empty. If a drive in the array fails, the data from the failed disk is

automatically rebuilt to the empty or “spare” disk.

Applications

In RAID 3+Spare disk failure does not require

immediate attention because the system re-

builds itself using the hot spare, but the failed

disk should be replaced as soon as possible.

RAID 3+ Spare

Disk 1 Disk 2 Disk 3 Disk 4

Ap(1-2)

Ap(3-4)

Bp(1-2)

Bp(3-4)

Cp(1-2)

Cp(3-4)

Spare

LaCie Products with RAID 3+Space

LaCie 4big quadra✦

How RAID 3+Space Capacity Is

Calculated

Each disk in a RAID 3+Spare system should

have the same capacity.

Storage capacity in a RAID 3+Spare conﬁgu-

ration is calculated by subtracting the number

of drives by two and multiplying by the disk

capacity, or

C = (n-2)*d

where:

C = available capacity

n = number of disks

d = disk capacity

For example, in a RAID 3+Spare array with four

drives each with a capacity of 1000GB, the to-

tal capacity of the array would be 2000GB:

C = (4-2)*1000

RAID 0

RAID 1

RAID 3

RAID 3+Spare

RAID 5

RAID 5+Spare

RAID 6

RAID 0+1

RAID 10

Concatenation

JBOD

RAID Selection

Page 6

LaCie RAID Technology White Paper

RAID 5

RAID 5 combines the striping of RAID 0 with data redundancy in an array with a minimum of three disks.

The difference between RAID 3 and RAID 5 is that a RAID 3 conﬁguration will offer better performance at the

expense of slightly less overall capacity. Data is striped across all disks and a parity block (P) for each data

block is written on the same stripe. If one physical disk fails, the data from the failed disk can be rebuilt onto a

replacement disk. No data is lost in the case of a single disk failure, but if a second disk fails before data can

be rebuilt to a replacement drive, all data in the array will be lost.

RAID 5

Disk 1 Disk 2 Disk 3 Disk 4

Applications

RAID 5 combines data safety with efﬁcient use

of disk space. Disk failure does not result in a

service interruption because data is read from

parity blocks. RAID 5 is useful for archiving

and for people who need performance and

constant access to their data, like video edi-

tors.

LaCie Products with RAID 5

LaCie 4big quadra✦

LaCie 5big network✦

How RAID 5 Capacity Is Calculated

Each disk in a RAID 5system should have the

same capacity.

Storage capacity in a RAID level 5 conﬁgura-

tion is calculated by subtracting the number

of drives by one and multiplying by the disk

capacity, or

C = (n-1)*d

where:

C = available capacity

n = number of disks

d = disk capacity

For example, in a RAID 5 array with four drives

each with a capacity of 1000GB, the total ca-

pacity of the array would be 3000GB:

C = (4-1)*1000

RAID 0

RAID 1

RAID 3

RAID 3+Spare

RAID 5

RAID 5+Spare

RAID 6

RAID 0+1

RAID 10

Concatenation

JBOD

RAID Selection

Page 7

LaCie RAID Technology White Paper

RAID 5+Spare

RAID 5+Spare, is a RAID 5 array in which one disk is used as spare to rebuild the system as soon as a disk

fails. At least four disks are required.

If one physical disk fails, the data remains available because it is read from the parity blocks. Data from a failed

disk is rebuilt onto the hot spare disk. When a failed disk is replaced, the replacement becomes the new hot

spare. No data is lost in the case of a single disk failure, but if a second disk fails before the system can rebuild

data to the hot spare, all data in the array will be lost.

Applications

The main advantage of RAID 5+Spare is that us-

ers can continue to access data even while the

data is rebuilt to the spare drive. RAID 5+Spare

has good data safety but disk space is limited by

the presence of the hot spare which is not used un-

til one of the other disks fails. Disk failure does not

require immediate attention because the system

rebuilds itself using the hot spare, but the failed

disk should be replaced as soon as possible.

RAID 5+Spare

Disk 1 Disk 2 Disk 3 Disk 4

Spare

Cp C2

LaCie Products with RAID 5+Spare

LaCie 4big quadra✦

LaCie 5big network✦

How RAID 5+Space Capacity Is

Calculated

Each disk in a RAID 5+Spare system should

have the same capacity.

Storage capacity in a RAID 5+Spare conﬁgu-

ration is calculated by subtracting the number

of drives by two and multiplying by the disk

capacity, or

C = (n-2)*d

where:

C = available capacity

n = number of disks

d = disk capacity

For example, in a RAID 5+Spare array with four

drives each with a capacity of 1000GB, the to-

tal capacity of the array would be 2000GB:

C = (4-2)*1000

RAID 0

RAID 1

RAID 3

RAID 3+Spare

RAID 5

RAID 5+Spare

RAID 6

RAID 0+1

RAID 10

Concatenation

JBOD

RAID Selection

Page 8

LaCie RAID Technology White Paper

RAID 6

In RAID 6, data is striped across all disks (minimum of four) and a two parity blocks for each data block (p and

q in the diagram at right) is written on the same stripe. If one physical disk fails, the data from the failed disk

can be rebuilt onto a replacement disk. This Raid mode can support up to two disk failures with no data loss.

RAID 6 provides for faster rebuilding of data from a failed disk.

Applications

RAID 6 provides data reliability with the addi-

tion of efﬁcient rebuilding in the case of a failed

drive. RAID 6 is therefore useful for people who

need serious security with less of an emphasis

on performance.

LaCie Products with RAID 6

LaCie 5big network✦

RAID 6

Disk 1 Disk 2 Disk 3 Disk 4 Disk 5

How RAID 6 Capacity Is Calculated

Each disk in a RAID 6 system should have the

same capacity.

Storage capacity in a RAID 6 conﬁguration is

calculated by subtracting the number of drives

by two and multiplying by the disk capacity,

C = (n-2)*d

where:

C = available capacity

n = number of disks

d = disk capacity

For example, in a RAID 6 array with ﬁve drives

each with a capacity of 1000GB, the total ca-

pacity of the array would be 3000GB:

C = (5-2)*1000

RAID 0

RAID 1

RAID 3

RAID 3+Spare

RAID 5

RAID 5+Spare

RAID 6

RAID 0+1

RAID 10

Concatenation

JBOD

RAID Selection

Page 9

LaCie RAID Technology White Paper

NESTED RAID LEVELS

RAID 0+1

RAID 0+1 is a secure RAID mode that is composed of a mirror of striped sets. RAID 0+1 arrays should have

disks in multiples of four. For LaCie products with ﬁve disks, in a RAID 0+1 array, the ﬁfth disk will either be a

spare or will be unused. In the diagram, at right, array B is a mirror of array A.

Up to two disks can fail in a RAID 0+1 array without loss of data, as long as the failed disks are not part of dif-

ferent RAID 0 pairs. In reference to the diagram, disk 1 and disk 2 could fail and the data would be preserved

on disks 3 and 4.

Applications

RAID 0+1 provides good speeds because of

RAID 0 striping, but cuts the available capacity

of a device in half (assume all disks in the array

have the same capacity).

LaCie Products with RAID 0+1

Currently, no LaCie products✦

RAID0 RAID0

RAID 0+1

A B

Disk 1 Disk 2 Disk 3 Disk 4

RAID1

How RAID 0+1 Capacity Is Calculated

Each disk in a RAID 0+1 system should have

the same capacity.

Storage capacity in a RAID 0+1 conﬁguration

is calculated by multiplying the number of drives

by the disk capacity and dividing by 2, or

C = n*d/2

where:

C = available capacity

n = number of disks

d = disk capacity

For example, in a RAID 0+1 array with four

drives each with a capacity of 1000GB, the

total capacity of the array would be 2000GB:

C = (4*1000)/2

RAID 0

RAID 1

RAID 3

RAID 3+Spare

RAID 5

RAID 5+Spare

RAID 6

RAID 0+1

RAID 10

Concatenation

JBOD

RAID Selection

Page 10

LaCie RAID Technology White Paper

RAID 1 RAID 1

RAID 0

RAID 10

Disk 1 Disk 2 Disk 3 Disk 4

RAID 10

RAID 10 (also called RAID 1+0) is another RAID level that combines the attributes of other levels, speciﬁcally

RAID 1 and RAID 0. It is a “stripe of mirrored sets”, meaning that data is striped across two mirrored arrays.

The Striping occurs between arrays and the mirroring occurs within the same array, which makes the rebuilding

very fast. RAID 10 arrays should have disks in multiples of four. For LaCie products with ﬁve disks, in a RAID

10 array, the ﬁfth disk will either be a spare or will be unused. See the diagram at right.

In a RAID 10 array, one disk from each mirrored pair can fail with no data loss. However, the working disk in

an array with a failed disk becomes a weak point for the entire array. If the second disk in a mirrored pair fails,

the entire array is lost.

Applications

RAID 10 provides good speeds because of

RAID 0 striping, but cuts the available capacity

of a device in half (assuming all disks in the

array have the same capacity).

LaCie Products with RAID 10

LaCie 4big quadra✦

LaCie 5big network✦

How RAID 10 Capacity Is Calculated

Each disk in a RAID 10 system should have the

same capacity.

Storage capacity in a RAID 10 conﬁguration is

calculated by multiplying the number of drives

by the disk capacity and dividing by 2, or

C = n*d/2

where:

C = available capacity

n = number of disks

d = disk capacity

For example, in a RAID 10 array with four

drives each with a capacity of 1000GB, the

total capacity of the array would be 2000GB:

C = (4*1000)/2

RAID 0

RAID 1

RAID 3

RAID 3+Spare

RAID 5

RAID 5+Spare

RAID 6

RAID 0+1

RAID 10

Concatenation

JBOD

RAID Selection

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Table des matières

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