[Iometer-user] Linux numbers question...

[Ian <io...@ze...>]

I recently ran a series of tests on a remote linux server and had some
questions related to the tests.

First off, here is the access list settings:
File Server Access Pattern Linux,0
'size,% of size,% reads,% random,delay,burst,align,reply
4096,80,80,100,0,1,0,0
8192,2,80,100,0,1,0,0
16384,4,80,100,0,1,0,0
32768,4,80,100,0,1,0,0
65536,10,80,100,0,1,0,0

Under Test Setup I created an oustanding i/o range of 1 to 16 Power 2
(Exponential).

This was on an ext3 partition. (Prepared)

During the entire test, I had 'iostat -xd  1' running on the linux server
and thoughout the test, the numbers changed little:
(At the beginning of the test)
Device:,rrqm/s,wrqm/s,r/s,w/s,rsec/s,wsec/s,rkB/s,wkB/s,avgrq-sz,avgqu-sz=
,await,svctm,%util
sda,0.00,10.10,183.84,21.21,2763.64,719.19,1381.82,359.60,16.99,1.13,5.48=
,4.93,101.01

(At the end of the test)
Device:,rrqm/s,wrqm/s,r/s,w/s,rsec/s,wsec/s,rkB/s,wkB/s,avgrq-sz,avgqu-sz=
,await,svctm,%util
sda,0.00,0.00,104.04,25.25,2125.25,444.44,1062.63,222.22,19.88,1.01,7.81,=
7.84,101.41

The number I've got a question about is the avgqu-sz (Average Queue Size)
which always stayed at 1.  I had expected that to climb as the i/o's
stepped  up higher, but I'm proabably not understanding what these number=
s
truely represent.  It seemed that while the drive was being utilized to
it's fullest (It always stayed at 100%), I was unable to get the system t=
o
"hurt" so to speak by causing large queues and wait times, nor did I see
any large spikes in data per second (as far as iostat reported). I'm goin=
g
to run the test again, this time with a range if 1 to 128 to see if that
has any difference.

(Here's the definitions for each of those numbers)
rrqm/s: The number of read requests merged per second that were queued to
the device.

wrqm/s: The number of write requests merged per second that were queued t=
o
the device.

r/s: The number of read requests that were issued to the device per secon=
d.

w/s: The number of write requests that were issued to the device per seco=
nd.

rsec/s: The number of sectors read from the device per second.

wsec/s: The number of sectors written to the device per second.

rkB/s: The number of kilobytes read from the device per second.

wkB/s: The number of kilobytes written to the device per second.

avgrq-sz: The average size (in sectors) of the requests that were issued
to the device.

avgqu-sz: The average queue length of the requests that were issued to th=
e
device.

await: The  average  time (in milliseconds) for I/O requests issued to th=
e
device to be served.  This includes the time spent by the requests in
queue and the time spent servicing them.

svctm: The  average  service  time  (in  milliseconds) for I/O requests
that were issued to the device.

%util:  Percentage of CPU time during which I/O requests were issued to=20
the  device  (bandwidth utilization  for the device). Device saturation
occurs when this value is close to 100%.