HP RP7 Retail System Model 7100 Bedienungsanleitung PDF herunterladen (Seite 7)

Technical white paper | AHCI and RAID on HP EliteDesk and EliteOne 800 Business PCs

RAID 1 has redundancy and hence is a true RAID. It more than doubles reliability because the MTBF of RAID 1 is equal to the

MTBF of an individual drive multiplied by the number of drives (2). In other words, the probability of one hard drive failure on

a given day is the square root of that same probability. Hypothetically, if the chance for a single hard drive failure is 1:2000,

then the chance that both hard drives failing in RAID 1 is 1:4,000,000.

Mirroring, segmentation, and striping have no real meaning in RAID 1. In the table and graphic, the data is arranged in rows

for representation of different pieces of data.

Table 3. RAID 1 with two hard drives (mirrored).

First disk

Second disk

Data Segment 1 Data Segment 1

Data Segment 2 Data Segment 2

Data Segment 3 Data Segment 3

Data Segment 4 Data Segment 4

Data Segment 5 Data Segment 5

Data Segment 6 Data Segment 6

Data Segment 7 Data Segment 7

Data Segment 8 Data Segment 8

In Table 3, each “Data Segment n” represents a group of data, known as a strip. In this case, each row represents a stripe.

This table shows how information is duplicated in both hard drives. The size of the strips is mostly irrelevant and not a

configurable option.

To illustrate the concept of RAID 1 and mirroring, Figure 3 shows how a sequence of data “ABCD...” is stored in a RAID 1

volume. In this example, each letter represents a data segment. The graphic shows how the various pieces are replicated for

both of the hard drives; hence, if any one member of the RAID 1 volume fails, the information is kept in the surviving

members. After a hard drive failure, the user interface sends a notification so the failed hard drive can be replaced. No user

information is lost in this scenario.

A B C D …

…

HDD 1 HDD 2

Figure 3. Reliability – RAID 1 with two HDDs

1 2 3 4 5 6 7 8 9 10 11 12 ... 26 27

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HP RP7 Retail System Model 7100 Bedienungsanleitung Seite 7