On Sat, 3 Jan 2009, Roger Heflin wrote:
Matt Garman wrote:
When using Linux software RAID, I was thinking that, from a
performance perspective, the southbridge/SATA controller is probably
one of the most important components (assuming a reasonable CPU).
Is this a correct generalization?
If it is, has anyone done a study or benchmarked SATA controller
performance? Particularly with consumer-grade hardware?
I haven't been able to find much info about this on the web; the
Tech Report seems to consistently benchmark SATA performance:
AMD SB600: http://techreport.com/articles.x/13832/5
AMD SB700: http://techreport.com/articles.x/14261/10
AMD SB750: http://techreport.com/articles.x/13628/9
Intel ICH10: http://techreport.com/articles.x/15653/9
nVidia GeForce 8300: http://techreport.com/articles.x/14993/9
In general those benchmarks are mostly useless for Raid.
The biggest different for RAID is what happens when multiple channels are
used. On full speed streaming read/write almost every (even the worst PCI
controllers on a PCI bus) sata controller is close to equal when you only
have one drive, once you use 2 drives or more things change. If the given
controller setup can actually run several drives at close to full single
drive speed performance will be good, if it cannot things are going to get
much slower.
One test I do is a single dd from one disk and watch the io speed, and then I
add dd's and watch what happens. I have 4 identical disks, 2 are on a ICH7,
2 are on a pci bus based MB controller, any single of these disks will do
about 75MB/second no matter were it is, using 2 on the ich7 gets about
140-150MB/second, using the 2 on the pci bus based MB controller gets
98MB/second. If all of the controllers techreports tested were equal on
this test, then it might be worth it to look at the benchmarks techreport is
using, but the simple dd benchmark is likely more important, and I am pretty
sure that someone could use a controller (on a bandwidth limited bus) that
would do good on the above techreport benchmark, but fail horribly when
several disks with a high io speed were being used and work badly for raid.
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This has been discussed before, on the southbridge it is usually good/you
will get the maximum bandwidth for each of the 6 sata ports. After that,
you need to use PCI-e lanes from the northbridge. Using PCI-e x1 slots
that come off the southbridge can degrade performance of the 6 SATA ports
or the speed coming off the drives connected to the x1 slots will be slow.
What are you trying to accomplish?
As Roger pointed out, doing a dd is a good way to test, from each disk,
simultaneously, on an old Intel P965 board I was able to achieve
1.0-1.1Gbyte/sec doing that with 12 Velociraptors and 1.0Gbyte/sec reads
on the XFS filesystem when dd (reading) large data on the volume. Approx
500-600MiB/s from the southbridge, the other 400MiB/s from the
northbridge.
Justin.
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