HP NetRAID Installation and Configuration Guide

Glossary
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than a single disk can supply or accept it. While data is being transferred from
the first disk, the second disk can locate the next segment. Data striping is used
in some modern databases and in certain RAID devices.
Virtual Sizing: This setting, when enabled for a logical drive, causes the
controller to report the logical drive size larger than the actual physical capacity.
The "virtual" space allows for online capacity expansion.
Write Policy: When the processor writes to main memory, the data is first
written to the cache on the assumption that the processor will probably read it
again soon. The two Write policies for HP NetRAID are:
• Write Back: In a write-back cache, data is written to main memory only
when it is forced out of the cache. Write-back requires the cache to initiate
a main memory write of the flushed entry, followed (for a processor read)
by a main memory read. Write-back is efficient, because an entry may be
written many times in the cache without a main memory access.
• Write Through: In a write-through cache, data is written to main
memory at the same time as it is cached. Write-through is simpler than
write-back, because an entry that is to be replaced can be overwritten in
the cache, as it will already have been copied to main memory. Write-
Through is the recommended write policy for HP NetRAID-1Si adapter,
because this adapter does not have a battery backup unit.