in this game you get what you pay for.
you pay more money you get things that work better.
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disc systems have both a sequential access disc speed and a random access disc speed.
if you take this page as an example-
http://www.barefeats.com/hard88.html
everyone keeps going on about how this disc or that disc does 200MB/s.....buts thats with a single file - that is read sequentially in one go. All these disc tests measuring a single large file are a mirage.
The reality is that when you ask a disc to do 2 things at once - ( catalyst needs each playback layer to work at the same time ) - most of these sata discs and disc systems have terrible performance.
Sata discs have very poor latency - when asked to do 2 things at once - they have long delays.
Doesnt matter how many discs you connect together in a RAID - they still dont work well when asked to do more than one thing at a time.
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A chart like the one shown below - which is from
storagereview.com - shows random access file performance across multiple disc types.
And it shows most normal sata drives at 90, raptor at 130, and best scsi at 250.