Huawei OceanStor S5600 Initial Configuration Manual page 70

3 Configuring the Storage System
Parameter
Cache Prefetch
Policy
Cache Write Policy
3-16
Description
This parameter is defined to improve the read performance. Its options
are described as follows:
Constant prefetch
l
The size of the data to be prefetched is equal to the size as set. This
option applies to the applications that require reading data of a fixed
size in a certain order. An example is the streaming media on demand
by multiple subscribers who use the same bit rate.
Variable prefetch
l
The size of the data to be prefetched is the multiple for prefetching
multiplied by the length of a read command. This option applies to
the applications that require reading data of a variable size in a certain
order or to the situations where multiple subscribers read data
concurrently but no fixed prefetch size can be set, because the amount
of pre-read data cannot be judged. An example is the streaming media
on demand by multiple subscribers who use different bit rates.
Intelligent prefetch
l
The system software calculates a proper size of prefetched data. The
strategy is used in the read application of a single stream or when you
do not know whether data is read in sequence. For example, it is used
in reading or writing a file.
No prefetch
l
The prefetch function is disabled. The strategy is used in a random
read application or prefetched read application, such as a database
application.
NOTE
If you are familiar with the applications of the product, set this parameter to
Constant or Variable as required. In other cases, set this parameter to
Intelligent.
This parameter indicates how to write the cache. Its options are
described as follows:
Write Through Cache
l
Data is written in the cache while it is written in a disk. The host
accesses the disk during each write operation. This policy has low
performance and high reliability.
Write back and mirroring
l
Data is written in the local cache and the peer cache. This strategy
has high performance and reliability.
Write back and no mirroring
l
Data is written in the local cache only. This strategy has high
performance and general reliability.
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OceanStor S5600 Storage System
Initial Configuration Guide
Issue 02 (2009-09-30)