Raid1; Raid5 - NEC N8103-89 User Manual

2-3. RAID1

In the RAID1 level, data saved in a HDD is recorded to another HDD without change. The
mode is called "mirroring."
When data is recorded to a single HDD, the same data is recorded to another HDD. If
either of the HDDs is defected, the other HDD containing the same data can substitute for
the defected HDD. Thus the system can continue to operate without interruption.

2-4. RAID5

In RAID5, data is distributed to HDDs by striping and, at the same time, the parity
(redundant data) is distributed to the HDDs. This mode is called "striping with distributed
parity."
Each of stripe x, stripe x+1, and parity (x, x+1) created from stripe x and stripe x+1 is
recorded to a specific HDD. Accordingly, the total capacity assigned to the parity is just the
same as the capacity of a single HDD. If any one of the HDDs configuring a logical drive is
defected, data is still available without problems.
Disk array controller
Disk 1
Stripe 1
Stripe 2
Disk array controller
Disk 1
Stripe 1
Parity (3, 4)
Stripe 4
Parity (5, 6)
Disk 2
Stripe 1
Stripe 2
Disk 2 Disk 3
Stripe 2
Parity (1, 2)
Stripe 5
Stripe 3
Stripe 6
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