The default settings are suitable for reading a track for real time
playback. The server can also answer several client requests for several CDs in
different drives, provided the server computer is equipped with sufficient RAM,
several SCSI buses, and a fast network connection. Nevertheless, the server
configuration needs to be adjusted, if parallel access to several tracks of the
same CD or several CDs with only one drive available is desired.
Simultaneous accesses put down the overall data rate. The drive will spend some
time on positioning from track to track, or, even worse, on exchanging CDs. By
adjusting the cache settings appropriately the administrator can force the
server to read CD data in large chunks. This will increase the data throughput,
but can lead to delays for the clients. For example a client might wait for the
server to cache a complete track to avoid later CD changes. So if you plan to
have simultaneous acesses to a drive you should not play the audio tracks
through the file system, but copy them to the client and play them.
The audio file system makes use of the data cache. A volatile cache is the best
choice when it comes to reading large tracks that are needed only for a short
period of time. The data cache configuration is described in the section "The
data cache" on page 38.
The amount of data written to the cache when first accessing an audio track
depends on two parameters, atrack and rahead. When accessing
the first byte the server caches rahead chunks with atrack
blocks each (2352 bytes). To cache a track completely these parameters should
be changed so that rahead*atrack*2352 is greater than the
track size in bytes. Of course, the cache needs to be big enough, and even
bigger if several tracks should be cached at once. When using a very large
volatile cache, the swapspace or pagefile should be increased appropriately.