Re: pitiful performance of an SATA150 drive

From: Rink Springer <rink_at_il.fontys.nl>
Date: Wed, 1 Mar 2006 21:57:07 +0100
> I believe that linux uses bufferring in  their 'raw' disks so that you 
> may be actually doing larger
> reads and writes than you know.. (of course my knowledge of Linux is a 
> bit old so
> they may have changed that)

Linux 2.5+ will always queue I/O requests in PAGE_SIZE chunks (4KB on
i386) or less. These tiny requests will be concatinated by the disk
elevator if possible; for example, reading 64KB from block 0 once would
result in requesting 16 times 4KB, which will be translated to a single
"Read 64KB from block 0" request.

Therefore, the PAGE_SIZE cache (also known as the buffer cache, which
was merged with the page cache in the 2.5 tree) does not hurt
performance one bit.

I have no clue what FreeBSD does on this end.

-- 
Rink P.W. Springer                                - http://rink.nu
  "Richter: Tribute? You steal men's souls, and make them your slaves!
   Dracula: Perhaps the same could be said of all religions."
 - Castlevania: Symphony of the Night
Received on Wed Mar 01 2006 - 19:59:17 UTC

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