Acer SmartRAID V Bedienungsanleitung PDF herunterladen (Seite 178)

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Theory of Operation

Flush Strategy

DPT SmartRAID V controllers continually flush all dirty cache pages to

disk, with bursts occurring every second and increasing to 4 times per

second as the number of dirty pages increases. The data is written to disk

in elevator sorted order. The cache flushing routine establishes a flush

rate that writes all the dirty pages to disk within three minutes. If there is

no host activity, the cache flush will occur in less than three minutes.

Predictive Caching Algorithms

SmartRAID V predictive caching dramatically increases disk read

performance in computer systems with highly fragmented file structures.

The SmartRAID V pattern recognition algorithms are capable of

predicting disk read requests from the host computer by recognizing

patterns within seemingly random disk accesses. The SmartRAID V

pattern recognition algorithms not only look for hidden sequential strings,

but also analyze historical read/write patterns to determine when the host

is accessing files that were previously paged out of host cache.

Virtual Cache

SmartRAID V controllers use virtual cache to track the patterns of data

access for the most recently accessed disk data without actually caching

that data. The collected information can then be used for more intelligent

predictive algorithms. Additionally, the use of virtual cache enables the

controller to track how many hits would have resulted from installing

more controller or host cache. Virtual cache does not actually use RAM.

Read Ahead

Because disk data is often grouped as contiguous sectors on the disk, it is

sometimes beneficial to continue to read sequential sectors into cache

following a sector that has been requested by the computer. The

SmartRAID V controller uses algorithms that analyze the pattern of disk

access, looking for cases where sequential I/O may be occurring. If it is

determined that a read command from the computer is part of a pattern of

sequential reads, the controller reads additional sequential sectors into

cache so that future read commands will result in cache hits.

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Acer SmartRAID V Bedienungsanleitung Seite 178