Avago Technologies MegaRAID SATA 150-4 (523) - Manual (Page 30)

2-8 Introduction to RAID
Copyright © 2003–2006 by LSI Logic Corporation. All rights reserved.
If a single disk drive fails, it can be rebuilt from the parity and the data
on the remaining drives. RAID level 5 combines distributed parity with
disk striping, as shown in
Figure 2.3 . Parity provides redundancy for one
drive failure without duplicating the contents of entire disk drives, but
parity generation can slow the write process.
Figure 2.3 Distributed Parity (RAID 5) Example
2.4.11 Disk Spanning
Disk spanning allows multiple physical drives to function like one big
drive. Disk spanning overcomes lack of disk space and simplifies storage
management by combining existing resources or adding relatively
inexpensive resources. For example, four 20 Gbyte drives can be
combined to appear to the operating system as a single 80 Gbyte drive.
Spanning alone does not provide reliability or performance
enhancements. Spanned logical drives must have the same stripe size
and must be contiguous. In
Figure 2.4 , RAID 1 arrays are turned into a
RAID 10 array.
Important: Make sure that the spans are in different backplanes, so
that if one span fails, you do not lose the whole array.
Table 2.1 Types of Parity
Parity Type Description
Dedicated The parity of the data on two or more disk drives is stored on
an additional disk.
Distributed The parity data is distributed across more than one drive in the
system.
Segment 1
Segment 7
Parity (9–12)
Segment 2
Segment 8 Segment 3
Segment 9
Parity (5–8)
Segment 4
Segment 10
Segment 5
Segment 11
Parity (1–4)
Segment 6
Segment 12
Note: Parity is distributed across multiple drives in the array.