[Veritas-bu] iostat during duplication - strange
2002-04-03 13:41:38
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So here I am, testing the I/O characteristics of my new buffer settings for
duplications. I'm doing an "iostat" and I see the following for the two
tape drives that are source and destination for this dup.
$ sudo iostat -xtnc 5 | egrep "rmt.[01]|wsvc"
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
32.0 0.0 8192.1 0.0 0.0 1.0 0.0 31.1 0 100 rmt/0
0.0 14.0 0.0 3584.0 0.0 0.6 0.0 45.4 0 63 rmt/1
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
31.2 0.0 7986.9 0.0 0.0 1.0 0.0 31.9 0 99 rmt/0
0.0 16.8 0.0 4300.6 0.0 0.7 0.0 38.7 0 65 rmt/1
r/s w/s kr/s kw/s wait actv wsvc_t asvc_t %w %b device
31.0 0.0 7935.8 0.0 0.0 1.0 0.0 32.1 0 100 rmt/0
0.0 16.4 0.0 4198.3 0.0 0.5 0.0 32.8 0 54 rmt/1
It's easy to see which is source and which is destination. The strange
thing, consistent over about 10 minutes of this, is the nearly 2-to-1
difference between read volume (kr/s) & write volume (kw/s).
My first thought was blocking factors for read and write were different but
the iostat man page says these columes are KBytes/sec not blocks/sec.
Next I speculated that it was read-ahead buffering but eventually the
buffers would be full and I'd see the volume turn around - which I haven't.
I've verified that this is the only source and destination tapes in use -
the other tapes in other drives are doing other work.
tpconfig has each of these devices with the same settings, /dev/rmt/[01]cbn.
I would expect input volumes to match output volumes since the compression
is taking on the device.
So the new quandry - why doesn't the read volume match the write volume?
BTW: Sol 2.6 master/media, VxNB 3.4.1.
-----------------------------------------------------------------------
Mark Donaldson - Sr. Systems Engineer
Experian EMS - Denver Colorado
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<P><FONT SIZE=3D2>So here I am, testing the I/O characteristics of my =
new buffer settings for duplications. I'm doing an =
"iostat" and I see the following for the two tape drives that =
are source and destination for this dup.</FONT></P>
<P><FONT SIZE=3D2>$ sudo iostat -xtnc 5 | egrep =
"rmt.[01]|wsvc"</FONT>
<BR><FONT SIZE=3D2> r/s w/s kr/s =
kw/s wait actv wsvc_t asvc_t %w %b device</FONT>
<BR><FONT SIZE=3D2> 32.0 0.0 8192.1 =
0.0 0.0 1.0 0.0 =
31.1 0 100 rmt/0</FONT>
<BR><FONT SIZE=3D2> 0.0 14.0 0.0 3584.0 =
0.0 0.6 0.0 45.4 =
0 63 rmt/1</FONT>
<BR><FONT SIZE=3D2> r/s w/s kr/s =
kw/s wait actv wsvc_t asvc_t %w %b device</FONT>
<BR><FONT SIZE=3D2> 31.2 0.0 7986.9 =
0.0 0.0 1.0 0.0 =
31.9 0 99 rmt/0</FONT>
<BR><FONT SIZE=3D2> 0.0 16.8 0.0 4300.6 =
0.0 0.7 0.0 38.7 =
0 65 rmt/1</FONT>
<BR><FONT SIZE=3D2> r/s w/s kr/s =
kw/s wait actv wsvc_t asvc_t %w %b device</FONT>
<BR><FONT SIZE=3D2> 31.0 0.0 7935.8 =
0.0 0.0 1.0 0.0 =
32.1 0 100 rmt/0</FONT>
<BR><FONT SIZE=3D2> 0.0 16.4 0.0 4198.3 =
0.0 0.5 0.0 32.8 =
0 54 rmt/1</FONT>
</P>
<P><FONT SIZE=3D2>It's easy to see which is source and which is =
destination. The strange thing, consistent over about 10 minutes =
of this, is the nearly 2-to-1 difference between read volume (kr/s) =
& write volume (kw/s). </FONT></P>
<P><FONT SIZE=3D2>My first thought was blocking factors for read and =
write were different but the iostat man page says these columes are =
KBytes/sec not blocks/sec. </FONT></P>
<P><FONT SIZE=3D2>Next I speculated that it was read-ahead buffering =
but eventually the buffers would be full and I'd see the volume turn =
around - which I haven't. </FONT></P>
<P><FONT SIZE=3D2>I've verified that this is the only source and =
destination tapes in use - the other tapes in other drives are doing =
other work.</FONT></P>
<P><FONT SIZE=3D2>tpconfig has each of these devices with the same =
settings, /dev/rmt/[01]cbn. I would expect input volumes to match =
output volumes since the compression is taking on the =
device.</FONT></P>
<P><FONT SIZE=3D2>So the new quandry - why doesn't the read volume =
match the write volume?</FONT>
</P>
<P><FONT SIZE=3D2>BTW: Sol 2.6 master/media, VxNB 3.4.1.</FONT>
</P>
<P><FONT =
SIZE=3D2>---------------------------------------------------------------=
--------</FONT>
<BR><FONT SIZE=3D2> Mark Donaldson - Sr. Systems =
Engineer</FONT>
<BR><FONT SIZE=3D2> Experian EMS - Denver Colorado</FONT>
<BR><FONT =
SIZE=3D2>---------------------------------------------------------------=
--------</FONT>
</P>
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