Raid 1 With Two Hard Drives (Mirror) - Compaq dc7800 - Convertible Minitower PC User Manual

RAID 1 with two hard drives (Mirror)

Because it is a very cost-effective way to increase system storage reliability and a great value proposition,
RAID 1 is the only RAID configuration that HP preconfigures for HP Compaq dc7800 Business PCs. RAID
1 provides high availability with minimal performance impact, as well as greater reliability compared to
a single hard drive configuration.
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. Hypo-
thetically, if the chances that a single hard drive fails is 1:2000, with RAID 1 the chance that both of your
hard drives fail 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 (Mirror)
First Disk
Data Segment 1
Data Segment 2
Data Segment 3
Data Segment 4
Data Segment 5
Data Segment 6
Data Segment 7
Data Segment 8
In the previous table, each "Data Segment n" represents a group of data, known as a strip. In this case,
each rows represent 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 better illustrate the concept of RAID 1 and mirroring, the following figure 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 mem-
ber 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.
Second Disk
Data Segment 1
Data Segment 2
Data Segment 3
Data Segment 4
Data Segment 5
Data Segment 6
Data Segment 7
Data Segment 8
7