Dell PowerEdge RAID Controller 5i - Manual (Page 15)

Overview
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RAID 1 uses disk mirroring so that data written to one physical disk is simultaneously written to another
physical disk. This is good for small databases or other applications that require small capacity, but
complete data redundancy.
RAID 5 uses disk striping and parity data across all physical disks (distributed parity) to provide high data
throughput and data redundancy, especially for small random access.
RAID 10, a combination of RAID 0 and RAID 1, uses disk striping across mirrored spans. It provides high
data throughput and complete data redundancy.
RAID 50, a combination of RAID 0 and RAID 5, uses distributed data parity and disk striping and works
best with data that requires high system availability, high request rates, high data transfers, and
medium-to-large capacity.
RAID Terminology
Disk Striping
Disk striping allows you to write data across multiple physical disks instead of just one physical disk. Disk
striping involves partitioning each physical disk storage space into stripes that can vary in size ranging
from 8 KB to 128 KB, often referred to as stripe size. These stripes are interleaved in a repeated
sequential manner. The part of the stripe on a single physical disk is called a strip.
For example, in a four-disk system using only disk striping (used in RAID level 0), segment 1 is written to
disk 1, segment 2 is written to disk 2, and so on. Disk striping enhances performance because multiple
physical disks are accessed simultaneously, but disk striping does not provide data redundancy.
Figure 1-1 shows an example of disk striping.
Figure 1-1. Example of Disk Striping (RAID 0)
Disk Mirroring
With mirroring (used in RAID 1), data written to one disk is simultaneously written to another disk. If
one disk fails, the contents of the other disk can be used to run the system and rebuild the failed physical
disk. The primary advantage of disk mirroring is that it provides 100 percent data redundancy. Because
the contents of the disk are completely written to a second disk, it does not matter if one of the disks
fails. Both disks contain the same data at all times. Either of the physical disks can act as the operational
physical disk.
Stripe element 1
Stripe element 5
Stripe element 9 Stripe element 2
Stripe element 6
Stripe element 10
Stripe element 3
Stripe element 7
Stripe element 11
Stripe element 4
Stripe element 8
Stripe element 12
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