For measuring latency and responsiveness, fio is a great tool. It's
by the maintainer of the Linux kernel's block layer. You can even
export its data easily to data analysis software like GNU R or a
python script that uses pandas.
There's a feature of the Linux kernel that I've never tried, but you
might be interested. The block layer has a tracing feature in
recent kernels, and there's a blktrace tool that works with it.
On 07/14/2014 10:00 PM, David &
Linda Leach wrote:
Killer,
That confirms some of my suspicion. In my testing I can see
requests for 1024 sectors (512K) of data from the hard drive
which the AoE client would have to carve up into individual
read/write requests that can fit into an AoE packet. At the
server, each of these requests would appear as individual
read/write requests of the disk so if you followed the optimal
packet usage for Ethernet for AoE you would end up with a
jumbo frame request for 17 sectors. The initial 1024 sector
request at the client would start on an aligned boundary for
the first two 4k "sectors" but then have a trailing 512 byte
sector request which will cause the next 7 requests to start
off unaligned and end aligned... so a 1024 sector request from
the host OS will result in only 1 out of 8 requests starting
on an aligned boundary.
Since the AoE client driver is handling disk requests from
the host OS, the host OS is going to assume certain things
about the disk and try to ensure proper alignment requests. I
even think I've seen that if you have an application that is
going to write to sector 1 that the host will read (or page)
in the 4k chunk starting at sector 0 and then write out the 4k
chunk at sector 0 with the modification of sector 1.
It seems like if we wanted to ensure alignment and support this
configurable "max sector count" request size that the size we
would want would be 16 to keep these large requests aligned and
to ensure maximum efficiency for disk usage at the server. But
this goes back to some of my original questions:
1) What is the test setup
to determine the results of changing the max request size?
2) How does one measure
latency and "responsiveness"?
David
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