Glossary; Disk Array Terms And Technologies - HP D5970A - NetServer - LCII Configuration Manual

Glossary

Disk Array Terms and Technologies

Array: An array of disk modules combines the storage space on the disk modules
into a single segment of contiguous storage space. The integrated HP NetRAID
controller can group disk modules on one or more of its SCSI channels into an
array. A hot spare disk module does not participate in an array.
Array Spanning: Array spanning by a logical drive combines storage space in
two, three, or four arrays of disk modules into the logical drive's single
contiguous storage space.
Logical drives of the integrated HP NetRAID controller can span consecutively
numbered arrays that each consist of the same number of disk modules. Array
spanning promotes RAID levels 1, 3, and 5 to RAID levels 10, 30, and 50,
respectively.
BIOS: (Basic Input/Output System) The part of the operating system of the
computer that provides the lowest level interface to peripheral devices.
Cache Policy: HP NetRAID lets you choose one of two cache policies:
Cached I/O: Reads will always be cached regardless of randomness, and
the selected Read policy (Read Ahead, Normal, or Adaptive) and Write
policy (Write-Through and Write-Back) applies.
Direct I/O: First reads to a new location will always come directly from
the disk. If a location is read repeatedly, then the Read policy (Read
Ahead, Normal, or Adaptive) as selected will apply and the read data will
be cached. Read data is cached only if accessed repeatedly. With 100%
random reads, nothing is cached.
Capacity Expansion (or Volume Expansion): Allows you to increase the size of
an existing volume while remaining online under Windows NT or Novell
NetWare. The controller creates virtual space when the "virtual sizing" option is
enabled in the Express Tools utility. A volume can then be expanded into the
virtual space by adding a physical disk through reconstruction. Reconstruction is
only permitted on a logical drive that occupies a single array and is the only
logical drive in the array. You cannot use online capacity expansion on logical
drives that span arrays (RAID levels 10, 30, or 50).
123