NEC BladeServer Express5800 Series User Manual page 89

4-32 Configuring Your Server
RAID1
In the RAID1 level, data saved in a HDD is written to another HDD without change. The mode is
called "mirroring".
When data is written onto a single HDD, the same data is written onto 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.
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 written onto 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 with no problems.
Disk array controller
HDD 1
Stripe 1
Stripe 2
Disk array controller
HDD 1
Stripe 1
Stripe 4
Parity (5, 6)
HDD 2
Stripe 2
Parity (3, 4)
Stripe 5
HDD 2
Stripe 1
Stripe 2
HDD 3
Parity (1, 2)
Stripe 3
Stripe 6