Gluster users - Sep 2017 - how to use cluster volume top command: correct usage?

Dear All,

in order to test my gluster volume performance, I started using gluster volume
top command, but something is not clear to me.
If I understand, gluster volume top command doesn?t measure in real time the
?weight? of my running workload, but it executed a ?dd? and mesaures the
corresponding throughput.

From the Admin Guide:

"Viewing List of Write Performance on each Brick

You can view list of write throughput of files on each brick. If brick name is
not specified, then the metrics of all the bricks belonging to that volume will
be displayed. The output will be the write throughput.
This command will initiate a dd for the specified count and block size and
measures the corresponding throughput. To view list of write performance on each
brick?"

So, I decided to start a first and simple top session like the following one:

[root at s01 ~]# gluster volume top tier2 write-perf bs 4096 count 1000 brick
s02-stg:/gluster/mnt3/brick list-cnt 10
Brick: s02-stg:/gluster/mnt3/brick
Throughput 1061.97 MBps time 0.0039 secs
MBps Filename                                        Time                      
==== ========                                        ====                      
 799 ...l1965_r1i1p1_1966100100-1966103118.nc.Pr1vPz 2017-09-18 17:10:50.593555
 780 ...l1965_r1i2p1_1966070100-1966073118.nc.1qr0Ad 2017-09-18 16:48:47.266599
 771 ...l1965_r1i1p1_1967080100-1967083118.nc.HnBJlN 2017-09-18 17:30:19.527468
 762 ...l1965_r1i2p1_1969090100-1969093018.nc.VJTT7X 2017-09-18 17:17:23.422664
 753 ...l1970_r1i2p1_1973020100-1973022818.nc.8vLPR6 2017-09-18 19:30:25.582939
 753 ...l1965_r1i1p1_1974040100-1974043018.nc.bjQbM5 2017-09-18 17:10:50.243065
 744 ...l1970_r1i2p1_1975030100-1975033118.nc.yL8RkY 2017-09-18 19:30:24.116164
 744 ...0_r1i1p1_197301010130-197312312230.nc.dusKKg 2017-09-18 19:07:43.755518
 744 ...l1965_r1i3p1_1971010100-1971013118.nc.NedbLU 2017-09-18 17:02:52.670703
 736 ...0_r1i2p1_197401010130-197412312230.nc.atE3Uf 2017-09-18 19:01:45.918796

But in the produced output I see some data files previously saved on the volume
and related MBps? and no other temporary file produced by ?dd?.
Anyone of you could please explain what does ?gluster volume top? command really
do and how to use it?

Thank you very much,
Mauro Tridici

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