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MegaRAID SAS Software User Guide Chapter 2: Introduction to RAID
| Components and Features
2.4.11 Disk Spanning Disk spanning allows multiple drives to function like one big drive. Spanning
overcomes lack of disk space and simplifies storage management by combining
existing resources or adding relatively inexpensive resources. For example, four 20 GB
drives can be combined to appear to the operating system as a single 80 GB drive.
Spanning alone does not provide reliability or performance enhancements. Spanned
virtual drives must have the same stripe size and must be contiguous. In Figure6, RAID
1 drive groups are turned into a RAID 10 drive group.
NOTE: Make sure that the spans are in different backplanes, so that if one span fails, you
do not lose the whole drive group.
Figure 6: Example of Disk Spanning
Spanning two contiguous RAID 0 virtual drives does not produce a new RAID level or
add fault tolerance. It does increase the capacity of the virtual drive and improves
performance by doubling the number of spindles.
2.4.11.1 Spanning for RAID 00,
RAID 10, RAID 50, and RAID 60
Table3 describes how to configure RAID 00, RAID 10, RAID 50, and RAID 60 by
spanning. The virtual drives must have the same stripe size and the maximum number
of spans is eight. The full drive capacity is used when you span virtual drives; you
cannot specify a smaller drive capacity.
See Chapter8, Configuration for detailed procedures for configuring drive groups and
virtual drives, and spanning the drives.
60 GB 60 GB
Can Be Accessed as
One 120-GB Drive
60 GB 60 GB
Can Be Accessed as
One 120-GB Drive
Table 3: Spanning for RAID 10, RAID 50, and RAID 60
Level Description
00 Configure RAID 00 by spanning two contiguous RAID 0 virtual drives, up to
the maximum number of supported devices for the controller.
10 Configure RAID 10 by spanning two contiguous RAID 1 virtual drives, up to
the maximum number of supported devices for the controller. RAID 10
supports a maximum of eight spans. You must use an even number of drives
in each RAID virtual drive in the span. The RAID 1 virtual drives must have
the same stripe size.
50 Configure RAID 50 by spanning two contiguous RAID 5 virtual drives. The
RAID 5 virtual drives must have the same stripe size.
60 Configure RAID 60 by spanning two contiguous RAID 6 virtual drives. The
RAID 6 virtual drives must have the same stripe size.
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