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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