Avago Technologies MegaRAID SATA 150-4 (523) - Manual (Page 29)

RAID Components and Features 2-7
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2.4.8.2 Stripe Size
The stripe size is the length of the interleaved data segments that the
RAID controller writes across multiple drives.
2.4.9 Disk Mirroring
With disk mirroring (used in RAID 1), data written to one disk is
simultaneously written to another disk. If one disk fails, the contents of the
other disk can be used to run the system and reconstruct the failed disk.
The primary advantage of disk mirroring is that it provides 100% data
redundancy. Because the disk contents are completely written to a second
disk, it does not matter whether one of the disks fails. Both disks contain
the same data at all times. Either drive can act as the operational drive.
Disk mirroring provides 100% redundancy, but is expensive because
each drive in the system must be duplicated.
Figure 2.2 shows an
example of disk mirroring.
Figure 2.2 Disk Mirroring (RAID 1) Example
2.4.10 Parity
Parity generates a set of redundancy data from two or more parent data
sets. The redundancy data can reconstruct one of the parent data sets.
Parity data does not fully duplicate the parent data sets. In RAID, this
method is applied to entire drives or stripes across all disk drives in an
array. The types of parity are described in
Table 2.1 .
Segment 1
Segment 2
Segment 3 Segment 1 Duplicated
Segment 2 Duplicated
Segment 3 Duplicated
Segment 4 Segment 4 Duplicated