Re: RAIDframe performance vs. stripe size

[Greg Oster <oster%cs.usask.ca@localhost>]

On Sat, 12 May 2012 00:20:36 +0200
Edgar Fuß <ef%math.uni-bonn.de@localhost> wrote:

> > Does that help?
> Yes, thanks!
> 
> Yet another question: Suppose I have 4k fsbsize and a stripe size
> such that 16k go to one disc (i.e. 64k stripes with my 4+1 RAID 5
> example). Will RAIDframe ever deal with less than 16k? I.e.:
> 
> A. I read one 4k fs block. Will RAIDframe read 4k or 16k from the
> disc?

I think the answer to that is "It depends on if the filesystem does any
sort of read-ahead".  Ignoring any readahead, if applicable, I believe
RAIDframe will just read the 4k fs block.

> B. I write one 4k fs block. Will RAIDframe rmw two 4k chunks or two
> 16k chunks?

It's been a while since I've been in that code... At a quick glance
it looks like the answer is that it does it based on sectors.... So it
will manipulate the smallest number of sectors that it needs to in
order to get the job done... 

Later...

Greg Oster