gstripe small transaction size

Alexander Motin mav at FreeBSD.org
Tue Sep 28 05:45:41 UTC 2010


Stephen Sanders wrote:
>  I'm trying a disk throughput experiment where in two 3ware raid 6's are
> being put into a g_strip raid 0.
> 
> The raid 6's are using 8 7200RPM disks.  The disk transfer rate is
> ~80MB/s.  Using a load generation tool that is using O_DIRECT for I/O,
> I've generated the following short output from iostat.  Needless to say,
> the write performance is a lot less than I'm expecting.
> 
> We've modified the kernel such that our KB/t figure is closer to 512KB/t
> per disk when measured without the g_strip.  With g_strip turned on, the
> KB/t number is more like 60KB/t.
> 
> The question is how do I get g_stripe to write larger transactions to
> the disk ?

How old is your system? There was bug, fixed 8-12 months ago, making
fast mode in gstripe not working on systems with increased MAXPHYS. As I
understand, it is what you've changed in your kernel.

-- 
Alexander Motin


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