HP ProLiant High Availability Storage Servers User Manual download pdf (Page 25)

For more information on the different RAID levels, see Table 6.

Table 6 Descriptions of RAID levels

DescriptionRAID level

Offers no protection against disk failure. If a disk drive fails, data is

lost.

No RAID

Offers the greatest capacity and performance without data protection.

If you select this option, you will experience data loss if a hard drive

that holds the data fails. However, because no logical drive capacity

is used for redundant data, this method offers the best capacity. This

method offers the best processing speed by reading two stripes on

different hard drives at the same time and by not having a parity

drive.

RAID 0 – Striping (No Fault Tolerance)

Offers a good combination of data protection and performance. RAID

1 or drive mirroring creates fault tolerance by storing duplicate sets

of data on a minimum of two hard drives. There must be an even

number of drives for RAID 1. RAID 1 and RAID 1+0(10) are the most

costly fault tolerance methods because they require 50 percent of the

drive capacity to store the redundant data. RAID 1 mirrors the contents

of one hard drive in the array onto another. If either hard drive fails,

the other hard drive provides a backup copy of the files and normal

system operations are not interrupted.

RAID 1 – Mirroring

Offers the best combination of data protection and performance. RAID

1+0 or drive mirroring creates fault tolerance by storing duplicate sets

of data on a minimum of four hard drives. There must be an even

number of drives for RAID 1+0. RAID 1+0(10) and RAID 1 are the

most costly fault tolerance methods because they require 50 percent

of the drive capacity to store the redundant data. RAID 1+0(10) first

mirrors each drive in the array to another, and then stripes the data

across the mirrored pair. If a physical drive fails, the mirror drive

provides a backup copy of the files and normal system operations are

not interrupted. RAID 1+0(10) can withstand multiple simultaneous

drive failures, as long as the failed drives are not mirrored to each

other.

RAID 1+0 – Mirroring and Striping

Offers the best combination of data protection and usable capacity

while also improving performance over RAID 6. RAID 5 stores parity

data across all the physical drives in the array and allows more

simultaneous read operations and higher performance than data

guarding. If a drive fails, the controller uses the parity data and the

data on the remaining drives to reconstruct data from the failed drive.

The system continues operating with a slightly reduced performance

until you replace the failed drive. RAID 5 can only withstand the loss

of one drive without total array failure. It requires an array with a

minimum of three physical drives. Usable capacity is N-1 where N is

the number of physical drives in the logical array.

RAID 5 – Distributed Data Guarding

Offers the best data protection and is an extension of RAID 5. RAID

6 uses multiple parity sets to store data and can therefore tolerate up

to 2 drive failures simultaneously. RAID 6 requires a minimum of 4

drives and is available only if the controller has an enabler. Writer

performance is lower than RAID 5 due to parity data updating on

multiple drives. It uses two disk for parity; its fault tolerance allows

two disks to fail simultaneously. Usable capacity is N-2 where N is

the number of physical drives in the logical array.

RAID 6– Advanced Data Guarding

(ADG)

All-in-One Storage Manager 25

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