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Technology BackgroundPegasus3 Product Manual
RAID Controllers
RAID controller technology includes:
• Cache Policy (“Read Cache Policy” and “Write Cache Policy”)
• “Capacity Coercion”
As it is used with Pegasus, the term cache refers to any of several kinds of high- speed, volatile
memory that hold data moving from your computer to the physical drives or vice-versa. Cache is
important because it can read and write data much faster than a physical drive. There are read caches,
which hold data as it is read from a physical drive; and write caches, which hold data as it is written to a
physical drive.
In order to tune the cache for best performance in different applications, user- adjustable settings are
provided. Cache settings are made on the RAID controller. See “Making Controller Settings” on page
25.
Read Cache Policy
ReadCache– The read cache is enabled but no pre-fetch action.
ReadAhead– The read cache and predictive pre-fetch feature are enabled.
Read-ahead anticipates the next read and performs it before the request is made. Can increase
read performance.
NoCache– The read cache is disabled.
Write Cache Policy
WriteBack–Dataiswrittenrsttothecache,thentothelogicaldrive.
This provides better performance.
WriteThru– Also “Write Through.” Data is written to the cache and the logical drive at the same
time. This is safer.
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