User's Manual

Glossary 89
Read Policy
A controller attribute indicating the current read policy mode. In Always read
ahead
mode, the controller reads sequentially ahead of requested data and stores
the additional data in cache memory, anticipating that the data will be needed
soon. This speeds up reads for sequential data, but there is little improvement
when accessing random data. In
No read ahead mode, read-ahead capability is
disabled. In
Adaptive read ahead mode, the controller begins using read-ahead if
the two most recent disk accesses occurred in sequential sectors. If the read
requests are random, the controller reverts to
No read ahead mode.
rebuild
The regeneration of all data to a replacement disk in a redundant virtual disk
after a physical disk failure. A disk rebuild normally occurs without interrupting
normal operations on the affected virtual disk, though some degradation of
performance of the disk subsystem can occur.
rebuild rate
The percentage of central processing unit (CPU) resources devoted to
rebuilding data onto a new physical disk after a disk in a storage configuration
has failed.
reclaim virtual disk
A method of undoing the configuration of a new virtual disk. If you highlight
the virtual disk in the Configuration Wizard and click the
Reclaim button, the
individual disk drives are removed from the virtual disk configuration.
reconstruction rate
The user-defined rate at which a reconstruct operation is carried out.
redundancy
A property of a storage configuration that prevents data from being lost when
one physical disk fails in the configuration.
redundant configuration
A virtual disk that has redundant data on physical disks in the disk group that can
be used to rebuild a failed physical disk. The redundant data can be parity data
striped across multiple physical disks in a disk group, or it can be a complete
mirrored copy of the data stored on a second physical disk. A redundant
configuration protects the data in case a physical disk fails in the configuration.