HP StorageWorks EVA Controller HSG V8.8 Software - Manual (Page 137)

Glossary
137 Command Console V2.5 User Guide
RAID 3
RAID 3 virtual disks use parity for data redundancy. A RAID 3
virtual disk is a type of striped parity virtual disk.
In a RAID 0 virtual disk, host data is divided into strips spread
in a stripe across virtual disk member devices. An additional
strip for parity information is appended to each stripe. This
technique allows much faster read and write performance than
does reading and writing to a single device. A three-device,
RAID 3 virtual disk has potentially three times the bandwidth
of a single device because three separate, small pieces of host
data move in parallel.
In addition, because each data stripe is protected by parity
information, there is a significant level of data redundancy for
high availability. Some RAID 3 configurations use a dedicated
parity device, but most controllers intersperse the parity strips
within the data strips to maximize the read performance.
RAID 3 virtual disks provide high performance and high
availability at reasonable cost. They are optimal for use in
applications requiring relatively high data transfer rates and
having relatively low I/O request rates.
RAID 3/5
RAID 3/5 sets are enhanced stripesets – they use striping to
increase I/O performance and distributed-parity data to ensure
data availability.
RAID 3/5 sets are similar to stripesets in that the I/O requests
are broken into smaller “chunks” and striped across the disk
drives. RAID sets also create chunks of parity data and stripe
them across all members of the RAIDset. This parity data is
derived mathematically from the I/O data and enables the
controller to reconstruct the I/O data if a single disk drive fails.
Thus, it becomes possible to lose a disk drive without losing its
data it contained. Data can be lost, however, if a second disk
drive fails before the controller replaces the first failed disk
drive and reconstructs the data.