Lenovo ThinkServer RD240 MegaRAID SAS Software User Guide - Page 42
Disk Spanning, Example of Disk Spanning
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2.4.12 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 Figure 2.4, 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 2.4 Example of Disk Spanning 60 GB/s 60 GB/s Can Be Accessed as One 120 GB/s Drive 60 GB/s 60 GB/s Can Be Accessed as One 120 GB/s Drive Note: 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. 2.4.12.1 Spanning for RAID 00, RAID 10, RAID 50, and RAID 60 Table 2.2 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 Section Chapter 8, "Configuration" for detailed procedures for configuring drive groups and virtual drives, and spanning the drives. 2-10 Introduction to RAID
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