18
2.8 Parameters
The parameters menu is accessible from the main NumaRAID menu and sets out the
overall NumaRAID settings that will apply universally. The following settings are availa-‐
ble:
Maximum Read Ahead Distance in 128k Stripes:
When you playback video for exam-‐
ple, 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 cur-‐
rently 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 de-‐
fault 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 ex-‐
ample), 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 effec-‐
tive.
Stripes Required in Memory before Read Ahead Allowed:
This is the amount of se-‐
QOS 8-Bay User Manual
QOS Server is a subsidary of Ocean Tides Productions Ltd. © Copyright 2013
