Dell 6 series User Manual page 19

Figure 2-2 shows an example of disk mirroring.
Figure 2-2. Example of Disk Mirroring (RAID 1)
Stripe element 1 Stripe element 1 Duplicated
Stripe element 2 Stripe element 2 Duplicated
Stripe element 3 Stripe element 3 Duplicated
Stripe element 4 Stripe element 4 Duplicated
Spanned RAID Levels
Spanning is a term used to describe the way in which RAID levels 10, 50,
and 60 are constructed from multiple sets of basic, or simple RAID levels.
For example, a RAID 10 has multiple sets of RAID 1 arrays where each RAID 1
set is considered a span. Data is then striped (RAID 0) across the RAID 1
spans to create a RAID 10 virtual disk. If you are using RAID 50 or RAID 60,
you can combine multiple sets of RAID 5 and RAID 6 together with striping.
Parity Data
Parity data is redundant data that is generated to provide fault tolerance
within certain RAID levels. In the event of a drive failure the parity data can
be used by the controller to regenerate user data. Parity data is present for
RAID 5, 6, 50, and 60.
The parity data is distributed across all the physical disks in the system. If a
single physical disk fails, it can be rebuilt from the parity and the data on the
remaining physical disks. RAID level 5 combines distributed parity with disk
striping, as shown in Figure 2-3. Parity provides redundancy for one physical
disk failure without duplicating the contents of entire physical disks.
RAID 6 combines dual distributed parity with disk striping. This level of
parity allows for two disk failures without duplicating the contents of entire
physical disks.
19
Overview