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Re: Raidframe and disk strategy

On Thu, 9 Aug 2012 09:45:18 -0700 (Brian Buhrow) wrote:

>       Hello.  I'm not going to claim to be an expert at anything
> here, but grepping through the raidframe sources doesn't show me
> anything that says it sorts requests from the upper layers, nor that
> it sorts requests to the  underlying disks except in the case of when
> it's doing reconstruction or paritymap maintenance.  That said, and
> while I don't have any hard numbers yet, it looks like the patch I
> posted last night yields an instant 16% improvement on throughput on
> one of the backup servers I run. Could someone else try the patch and
> see if they see similar gains?  Below is a shell snippet I use
> in /etc/rc.local to set the strategy for all the attached raid sets
> on a system, in case that's useful for folks.

So there are a number of places sorting can occur here... 

 1) In the bufq_* strategy bits in RAIDframe.
 2) In the rf_diskqueue.c code, where we have fifo, cvscan, shortest
 seek time first, and two elevator algorithms as possible candidates
 for use in disk queueing.
 3) In the underlying component strategies (which may be another
 RAIDframe device, a CCD, vnd, sd, wd, or whatever).

The sorting stuff I was referring to in my previous email (where I said
it could be handled in the config file) was 2).  I wasn't even thinking
about 1).

Now if you're seeing a 16% performance boost, it's likely worth adding
the code you suggest -- it's not much code for a nice bump for folks
who might have a similar IO mix/setup.


Greg Oster

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