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Re: Raidframe and disk strategy

On Wed, 8 Aug 2012 15:07:24 -0700 (Brian Buhrow) wrote:

>       hello.  I've been looking at some disk performance issues
> lately and trying to figure out if there's anything I can do to make
> it better.  (This is under NetBSD/I386 5.1_stable with sources from
> July 18 2012).  During the course of my investigations, I discovered
> the raidframe driver does not implement the DIOCSSTRATEGY or
> DIOCGSTRATEGY ioctls.  Even more interestingly, I notice its set to
> use the fcfs strategy, and has been doing so since at least
> NetBSD-2.0.  The ccd(4) driver does the same thing. Presumably, the
> underlying disks can use what ever strategy they use for handling
> queued data, but I'm wondering if there is a particular reason the
> fcfs strategy was chosen for the raidframe driver as opposed to
> letting the system administrator pick the strategy?  My particular
> environment has a lot of unrelated reads and writes going on
> simultaneously, and it occurrs to me that using a different disk
> strategy than fcfs might mitigate some of these issues.  Were bench
> marks done to pick the best strategy for raidframe and/or ccd or is
> there some other eason I'm missing that implementing a buffer queue
> strategy on top of these devices is a bad idea? -thanks -Brian

The "FIFO" strategy was the one that seemed to be the best tested at
the time, and since I didn't want to introduce any more variables,
that's the one I went with as a default.  Unfortunately, the RAID
labels currently don't specify the queuing strategy, so the
'autoconfig' sets won't do anything other than FIFO at this time.
Non-autoconfig sets certainly support any of the other queuing
methods in the config file, and that could certainly be used for

If you'd like to write up support for alternate queuing methods being
specified by the component labels let me know -- it'd be one less thing
on my TODO list :) 


Greg Oster

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