Areca ARC-1880 Series User Manual page 145

WEB BROWSER-BASED CONFIGURATION
data access and stream. This feature is very useful for the video
streaming applications where there is high demand for constant
non-stop data flow with no interruption due to lower performance
of specific hardware.
• Amount of Read Ahead
Read-Ahead data is buffered in the RAID controller cache, howev-
er, thereby cutting down on the amount of I/O traffic to the disk.
The Amount of Read Ahead defines how many data of reading at
a time, making more efficient use of the RAID subsystem. This
makes it possible to locate and re-issue the data without repeti-
tive hard parsing activities.
The Amount of Read Ahead parameter is used to allocate an
amount of memory in the cache memory the frequently executed
queries and return the result set back to the host without real
disk read execution. Default value is Auto: Controller will base on
the HDD number to set the amount of Read Ahead value. You can
select between 512KB ~ 16MB.
• Number of AV Stream
RAID controllers are required to have not only the function of
processing ordinary data but also the function of dealing with AV
(audio/video) stream data needing real-time processing. Since
the bus cycle used in RAID controller was designed to transfer
the computer data exactly, it was unsuitable for the transfer of AV
stream needing great band widths. They are required to do some
setting for the handshaking during the processing of stream data.
This setting is an object of transferring stream data efficiently
on an existing RAID controller. Normally you should not need
to modify this value. Default value is 6. You can select between
6~256.
To decide how to set AV stream playout parameter, you need to
check the Number of Stream, Amount of Read Ahead, and Total
Cache Memory during runtime. You can try to adjust the three
numbers to get the best performance as your requirement. Num-
ber of Stream shows the number of stream added to the system,
Amount of Read Ahead shows the amount of Read Ahead data
taken from the cache without real disk execution, and Total Cache
Memory shows the total available memory being installed in the
RAID controller. The following is the rule of optimized setting for
the AV Stream Playout application.
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