On Sun, 4 Jan 2009, Matt Garman wrote:
On Sun, Jan 04, 2009 at 04:55:18AM -0500, Justin Piszcz wrote:
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.
So, in general, the ideal is to be able to simultaneously read/write
from multiple disks at the same speed as a single drive.
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.
Are you talking about using additional SATA controllers (i.e. via
add-on cards)? Or simply talking about the interconnect between the
southbridge and the northbridge?
Interconnect between northbridge and southbridge. When all 6 channels on
mobo are in use, speed from PCI-e x1 is ~80MiB/s, when you stop that access
from all 6 ports, I get ~120MiB/s.
I think you're talking about the former, i.e. the SATA controller
integrated in the southbridge generally ought to be fine, but if you
start adding additional controllers that hang off the south bridge,
their could be competition for bandwidth to the northbridge...
right? (And wouldn't the nvidia chips have an edge here, since they
have everything combined into one chip?)
Makes intuitive sense anyway; but in my case I'm really just curious
about the SATA controller integrated into the southbridge; not
concerned with additional SATA controllers.
What are you trying to accomplish?
Trying to determine what motherboard would be ideal for a home NAS
box AND have the lowest power consumption... the AMD solutions seem
to win on the power consumption front, but I'm not sure about the
performance.
How fast do you need? Gigabit is only ~100MiB/s. Are you buying a 10Gbps
card?
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.
Is the "parallel dd test" valid if I do a raw read off the device,
e.g. "dd if=/dev/sda of=/dev/null"? All my drives are already in an
md array, so I can't access them individually at the filesystem
level.
Yes. You do not need to access them at the filesystem level. Both RAW
and on the filesystem, my benchmarks were the same when reading from 10 disks
raw or reading in a large file with dd using XFS as the filesystem.
Justin.
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
