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RAID Software User’s Guide 7
Disk Striping
Disk striping writes data across all of the physical disks in the array into fixed size partitions or
stripes. In most cases, the stripe size is user-defined. Stripes do not provide redundancy but
improve performance since striping allows multiple physical drives to be accessed at the same
time. These stripes are interleaved in a repeated sequential manner and the controller knows
where data is stored. The same stripe size should be kept across RAID arrays.
Terms used with strip sizing are listed below.
• Strip size: One disk section
• Stripe size: Total of one set of strips across all data disks, not including parity stripes
• Stripe width: The number of disks involved
Disk Spanning
Disk spanning allows more than one array to be combined into a single virtual drive. The
spanned arrays must have the same stripe size and must be contiguous. Spanning alone does
not provide redundancy but RAID modes 10, 50, and 60 all have redundancy provided in their
pre-spanned arrays through RAID 1, 5, or 6.
Note: Spanning two contiguous RAID 0 drives does not produce a new RAID level or add fault tolerance.
It does increase the size of the virtual volume and improves performance by doubling the number of
spindles. Spanning for RAID 10, RAID 50, and RAID 60 requires two to eight arrays of RAID 1, 5,
or 6 with the same stripe size and that always uses the entire drive.
CPU Usage
Resource allocation provides the user with the option to set the amount of compute cycles to
devote to various tasks, including the rate of rebuilds, initialization, consistency checks, and
patrol read. Setting resource to 100% gives total priority to the rebuild. Setting it at 0% means
the rebuild will only occur if the system is not doing anything else. The default rebuild rate
is 30%.
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