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36 Introduction to RAID
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Spanning for RAID 10 or RAID 50
Table 2-1 describes how to configure RAID 10 and RAID 50 by spanning.
NOTE: Spanning two
contiguous RAID 0
logical drives does not
produce a new RAID level
or add fault tolerance. It
does increase the size of
the logical volume and
improves performance by
doubling the number of
spindles.
Parity
Parity generates a set of redundancy data from two or more parent data sets.
The redundancy data can be used to reconstruct one of the parent data sets.
Parity data does not fully duplicate the parent data sets. In RAID, this
method is applied to entire drives or stripes across all disk drives in an array.
The types of parity are shown in Table 2-2.
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. Parity provides redundancy for one drive failure without
duplicating the contents of entire disk drives, but parity generation can slow
the write process. A dedicated parity scheme during normal read/write
operations is shown in Figure 2-4.
Table 2-1. Spanning for RAID 10 and RAID 50
Level Description
10 Configure RAID 10 by spanning two contiguous RAID 1 logical drives.
The RAID 1 logical drives must have the same stripe size.
NOTE: Refer to Chapter 11 "PERC 3 BIOS Configuration
Utility" for the configuration procedure for spanning RAID 1
logical drives.
50 Configure RAID 50 by spanning two contiguous RAID 5 logical drives.
The RAID 5 logical drives must have the same stripe size.
NOTE: Refer to Chapter 11 "PERC 3 BIOS Configuration
Utility" for the configuration procedure for spanning RAID 5
logical drives.
Table 2-2. 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 all drives in the system.