IBM DS8000 User Manual page 50

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DS8000 User's Guide
Redundant array of independent disks (RAID) is a method of configuring multiple
disk drives in a storage subsystem for high availability and high performance. The
collection of two or more disk drives presents the image of a single disk drive to
the system. In the event of a single device failure, data can be read or regenerated
from the other disk drives in the array.
RAID implementation enables fault-tolerant data storage by storing the data in
different places on multiple disk drive modules (DDMs). By placing data on
multiple disks, input/output operations can overlap in a balanced way to improve
the basic reliability and performance of the attached storage devices.
Physical capacity can be configured as RAID 5, RAID 6 (only on the DS8000
series), RAID 10, or a combination of RAID 5 and RAID 10. RAID 5 can offer
excellent performance for most applications, while RAID 10 can offer better
performance for selected applications, in particular, high random write content
applications in the open systems environment. RAID 6 increases data protection by
adding an extra layer of parity over the RAID 5 implementation.
You can reconfigure RAID 5 disk groups as RAID 10 disk groups or vice versa.
RAID 5 overview
RAID 5 is a method of spreading volume data across multiple disk drives. The
DS8000 and DS6000 series supports RAID 5 arrays.
RAID 5 increases performance by supporting concurrent accesses to the multiple
DDMs within each logical volume. Data protection is provided by parity, which is
stored throughout the drives in the array. If a drive fails, the data on that drive can
be restored using all the other drives in the array along with the parity bits that
were created when the data was stored.
RAID 6 overview
RAID 6 is a method of increasing the data protection of arrays with volume data
spread across multiple disk drives. The DS8000 series supports RAID 6 arrays.
RAID 6 increases data protection by adding an extra layer of parity over the RAID
5 implementation. By adding this protection, RAID 6 can restore data from an
array with up to two failed drives. The calculation and storage of extra parity
slightly reduces the capacity and performance compared to a RAID 5 array. RAID
6 is particularly suitable for storage using archive class DDMs.
RAID 10 overview
RAID 10 provides high availability by combining features of RAID 0 and RAID 1.
The DS8000 and DS6000 series supports RAID 10 arrays.
RAID 0 increases performance by striping volume data across multiple disk drives.
RAID 1 provides disk mirroring which duplicates data between two disk drives.
By combining the features of RAID 0 and RAID 1, RAID 10 provides a second
optimization for fault tolerance.
RAID 10 implementation provides data mirroring from one DDM to another DDM.
RAID 10 stripes data across half of the disk drives in the RAID 10 configuration.
The other half of the array mirrors the first set of disk drives. Access to data is
preserved if one disk in each mirrored pair remains available. In some cases, RAID
10 offers faster data reads and writes than RAID 5 because it does not need to