Avago Technologies MegaRAID Fast Path Software - Manual (Page 32)

Page 32 LSI Corporation Confidential | July 2011
MegaRAID SAS Software User Guide Chapter 2: Introduction to RAID | RAID Levels
2.4.19 Enclosure Management Enclosure management is the intelligent monitoring of the disk subsystem by software,
hardware or both. The disk subsystem can be part of the host computer or can reside in
an external disk enclosure. Enclosure management helps you stay informed of events
in the disk subsystem, such as a drive or power supply failure. Enclosure management
increases the fault tolerance of the disk subsystem.
2.5 RAID Levels The RAID controller supports RAID levels 0, 00, 1, 5, 6, 10, 50, and 60. The supported
RAID levels are summarized in the following section.
In addition, the RAID controller supports independent drives (configured as RAID 0 and
RAID 00.) The following sections describe the RAID levels in detail.
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. RAID 1 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 any 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 8 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 RAID 5 only.