Re: RAID-5 streaming read performance

[Ming Zhang <mingz@ele.uri.edu>]

On Tue, 2005-07-12 at 22:52 -0400, Dan Christensen wrote:
> Ming Zhang <mingz@ele.uri.edu> writes:
> 
> > On Mon, 2005-07-11 at 11:11 -0400, Dan Christensen wrote:
> >> I was wondering what I should expect in terms of streaming read
> >> performance when using (software) RAID-5 with four SATA drives.  I
> >> thought I would get a noticeable improvement compared to reads from a
> >> single device, but that's not the case.  I tested this by using dd to
> >> read 300MB directly from disk partitions /dev/sda7, etc, and also using
> >> dd to read 300MB directly from the raid device (/dev/md2 in this case).
> >> I get around 57MB/s from each of the disk partitions that make up the
> >> raid device, and about 58MB/s from the raid device.  On the other
> >> hand, if I run parallel reads from the component partitions, I get
> >> 25 to 30MB/s each, so the bus can clearly achieve more than 100MB/s.
> >> 
> >> [...]
> >> 
> >> System:
> >> - Athlon 2500+
> >> - kernel 2.6.12.2 (also tried 2.6.11.11)
> >> - four SATA drives (3 160G, 1 200G); Samsung Spinpoint
> >> - SiI3114 controller (latency_timer=32 by default; tried 128 too)
> > 
> > only 1 card? 4 port? try some other brand card and try to use several
> > cards at the same time. i met some poor cards before.
> 
> Yes, one 4-port controller.  It's on the motherboard.
> 
> I thought that since I get good throughput doing parallel reads from
> the four drives (see above) that would eliminate the controller as the
> bottleneck.  Am I wrong?
> 

have u try the parallel write?


> Dan
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