Lenovo ThinkServer RD330, Software User'S Manual

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MegaRAID SAS Software User Guide Chapter 2: Introduction to RAID
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RAID Levels
2.5.1 Summary of RAID Levels
RAID 0 uses striping to provide high data throughput, especially for large files in an
environment that does not require fault tolerance.
RAID 1 uses mirroring so that data written to one drive is simultaneously written to
another drive. 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 drives (distributed parity) to provide
high data throughput, especially for small random access.
RAID 6 uses distributed parity, with two independent parity blocks per stripe, and disk
striping. A RAID 6 virtual drive can survive the loss of two drives without losing data. A
RAID 6 drive group, which requires a minimum of three drives, is similar to a RAID 5
drive group. Blocks of data and parity information are written across all drives. The
parity information is used to recover the data if one or two drives fail in the drive group.
A RAID 00 drive group is a spanned drive group that creates a striped set from a series
of RAID 0 drive groups.
RAID 10, a combination of RAID 0 and RAID 1, consists of striped data across mirrored
spans. A RAID 10 drive group is a spanned drive group that creates a striped set from a
series of mirrored drives. RAID 10 allows 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. RAID 10 provides high data throughput and complete
data redundancy but uses a larger number of spans.
RAID 50, a combination of RAID 0 and RAID 5, uses distributed parity and disk striping.
A RAID 50 drive group is a spanned drive group in which data is striped across multiple
RAID 5 drive groups. RAID 50 works best with data that requires high reliability, high
request rates, high data transfers, and medium-to-large capacity.
NOTE: Having virtual drives of different RAID levels, such as RAID 0 and RAID 5, in the
same drive group is not allowed. For example, if an existing RAID 5 virtual drive is created
out of partial space in an array, the next virtual drive in the array has to be R5 only.
RAID 60, a combination of RAID 0 and RAID 6, uses distributed parity, with two
independent parity blocks per stripe in each RAID set, and disk striping. A RAID 60
virtual drive can survive the loss of two drives in each of the RAID 6 sets without losing
data. It works best with data that requires high reliability, high request rates, high data
transfers, and medium-to-large capacity.
2.5.2 Selecting a RAID Level
To ensure the best performance, you should select the optimal RAID level when you
create a system drive. The optimal RAID level for your drive group depends on a
number of factors:
 The number of drives in the drive group
 The capacity of the drives in the drive group
 The need for data redundancy
 The disk performance requirements