G A L A X Y ® A U R O U R A L S C O N F I G U R A T I O N A N D S Y S T E M I N T E G R A T I O N G U I D E
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Section 3 Management
3.1.9
PARAM Details
The PARAM functions are for setting or viewing global array parameters. Each row in each
table except for the last row of the last table, shows a parameter and value. Should you need
to change this value, you would alter the value on the right, then click the corresponding
update button on the left. It works the same way for changing every parameter. So here are
the parameters and what they mean/do:
Maximum Read Ahead Distance in 128k Stripes
: When you playback video for example,
you are essentially doing one large sequential read. To make playback smoother, the array
can be set to read more of the file than the position that the client computer is currently
requesting. This is called a read-ahead cache. The cache is only selectable in 128KB
increments, and the value here is the number of 128KB blocks to use (The blocks are referred
to as stripes, because they go across all of the drives in the RAID). The default value is 24.
This allows the computer to read 3MB ahead. So, for example, if you were playing a standard-
definition video file, which plays relatively slowly in relation of the array, when the computer
playing the video starts playing at 12MB of the file (for example), the array has already read
the next 3MB, and is ready to play up to 15MB, without doing any disk activity. As the
computer plays through this cache, it is refreshed with new data as necessary. Making this
setting it too high would cause kind of a stopping/starting of data reading on the array, and
setting it too low would render the cache not as effective.
