Avago Technologies 3ware SAS 9750-4i - Manual (Page 17)

Understanding RAID Levels and Concepts
www.lsi.com/channel/products 9
• Striping . Striping across disks allows data to be written and accessed on
more than one drive, at the same time. Striping combines each drive’s
capacity into one large volume. Striped disk arrays (RAID 0) achieve
highest transfer rates and performance at the expense of fault tolerance.
• Distributed Parity . Parity works in combination with striping on RAID 5,
RAID 6, and RAID 50. Parity information is written to each of the striped
drives, in rotation. Should a failure occur, the data on the failed drive can
be reconstructed from the data on the other drives.
• Hot Swap . The process of exchanging a drive without having to shut
down the system. This is useful when you need to exchange a defective
drive in a redundant unit.
• Array Roaming. The process of removing a unit from a controller and
putting it back later, either on the same controller, or a different one, and
having it recognized as a unit. The disks may be attached to different ports
than they were originally attached to, without harm to the data.
Available RAID Configurations
RAID is a method of combining several hard drives into one unit. It can offer
fault tolerance and higher throughput levels than a single hard drive or group
of independent hard drives. LSI's 3ware controllers support RAID 0, 1, 5, 6,
10, 50, and Single Disk. The information below provides a more in-depth
explanation of the different RAID levels.
RAID 0
RAID 0 provides improved performance, but no fault tolerance. Since the
data is striped across more than one disk, RAID 0 disk arrays achieve high
transfer rates because they can read and write data on more than one drive
simultaneously. The stripe size is configurable during unit creation. RAID 0
requires a minimum of two drives.
When drives are configured in a striped disk array (see Figure 1), large files
are distributed across the multiple disks using RAID 0 techniques.
Striped disk arrays give exceptional performance, particularly for data
intensive applications such as video editing, computer-aided design and
geographical information systems.
RAID 0 arrays are not fault tolerant. The loss of any drive results in the loss of
all the data in that array, and can even cause a system hang, depending on
your operating system. RAID 0 arrays are not recommended for high
availability systems unless additional precautions are taken to prevent system
hangs and data loss.