RAID 1 with two hard drives (Mirror))
Because it is a very
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 4: RAID 0 with two hard drives (Mirror)
First disk | Second disk |
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Data Segment 1 | Data Segment 1 |
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Data Segment 2 | Data Segment 2 |
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Data Segment 3 | Data Segment 3 |
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Data Segment 4 | Data Segment 4 |
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Data Segment 5 | Data Segment 5 |
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Data Segment 6 | Data Segment 6 |
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Data Segment 7 | Data Segment 7 |
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Data Segment 8 | Data Segment 8 |
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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, 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.
Figure 3: Reliability - RAID 1 mirroring
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