Richard;
Firstly, let me say that I welcome this discussion.
I was searching for comments and alternative viewpoints in the first
place and at the very least, people in the list and myself can learn and
understand the Solaris IO parameters better.
I did not make the assumption that maxphys overrides sd/ssd.conf
max_xfer_size. From the beginning I believe, you MAY have misunderstood
my email.
My objective is simple. Fabric attached high end storages like EMC have
stripe width around 8 Mbyte. Can we not match the SCSI transfer size to
be in or around the same size?
The original intention is to match the SCSI transfer size to the stripe
width of EMC arrays and other similar Fabric attached H/W RAID arrays.
I wanted to set maxphys=8388608 (8 Mbyte).
I fully realized that by setting maxphys=8388608 and NOT changing
sd/ssd.conf, the limit will still be determine by sd/ssd.conf maximum
transfer size, which is 1 Mbyte.
Thus I also suggested changing sd/ssd.conf to a higher value. Together
with relevant vxio and md parameters.
It is my impression that by changing the above values affects only
MAXIMUM transfer size and will not affect IO which have a smaller data
payload.
Am I wrong? At this point, I am unsure.
Examples of articles which recommends setting maxphys to 8388608 are
http://www.samag.com/documents/s=7667/sam0213b/0213b.htm
http://www.samag.com/documents/s=7610/sam0210j/0210j.htm
http://www.pluzzi.com/pluzzi/os/perf_tuning/solaris_8_performance_tuning.html
http://www.schuba.com/pub/courses/it454-ss2003/handouts/solaris_internals.pdf
Examples of articles which recommends setting maxphys to 2 Mbyte are;
http://people.ee.ethz.ch/~oetiker/tobjour/2003-02-12-09-00-f-1.html
All of the above articles also suggest setting the respective
sd/ssd.conf and md and vxio to more appropriate values to take advantage
of the larger maxphys.
I would love an "unofficial" non binding, in Good Faith answer from Sun
with respect to the above.
Warmest Regards
Steven Sim
Richard Elling wrote:
Richard;
I do believe I mention in my original email that the
default sd and ssd xfer is 1 Mbyte.
The problem, as I said, lies in the fact that maxphys is default 128
Mbyte which does not make sense especially since the sd/ssd driver
max_xfer_size is 1 Mbyte. (that includes ufs also!)
The limit of size of transfers is, for anything interesting, 1 Mbyte.
Perhaps you are making the assumption that maxphys overrides
the maximum transfer size dictated by the driver.
In almost all references to maxphys I have come across, almost all have
recommended that maxphys be set to 8388608 bytes as this improves large
transfers without affecting small IO.
First, write applications which make such large writes. The largest
write by a commercial application (I'm aware of) is 1 Mbyte.
I have a simple observation.
Solaris is an extremely powerful and scalabel OS but out of the box, the
IO settings is not appropriate for today's fibre attached storages.
Even setting the max transfer size to 1 PByte won't make any
difference until the applications do such large writes. But even
if you set it to 8 Mbytes, the protocol overhead per transfer is
so small that the performance gains will be barely noticeable.
In other words, AFAICT the current default has solved this
particular problem.
If properly tuned however, I do believe that it can outperform most
other general purpose OS.
We're trying :-) There is more fertile ground elsewhere.
Solaris 10 attempts to change this by removing many /etc/system
parameters. But for Solaris < 10......
Water under the bridge.
-- richard
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