Re: drive/block device write scheduling, buffer flushing?

[Rogier Wolff]

bert hubert wrote:
> On Wed, Jan 31, 2001 at 11:52:25AM -0500, Nathan Black wrote:
> > I was wondering if there is a way to make the kernel write to disk faster. 
> > I need to maintain a 10 MB /sec write rate to a 10K scsi disk in a computer,
> > but it caches and doesn't start writing to disk until I hit about 700 MB. At
> > that point, it pauses(presumably while the kernel is flushing some of the
> > buffers) and I will have missed data that I am trying to capture.
> 
> try opening with O_SYNC, or call fsync() every once in a while. Otherwise,
> this sounds like an application for a raw device, whereby you can write
> directly to the disk, with no caching in between.

But you'll probably need to use "buffer" too. 

   capture | buffer -m 128m > outputfile

Otherwise the "fsync" can block you for say 1/10th of a second,
causing loss of a few frames. (10MB per seconds sure sounds like
video).

Roger. 

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