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From: Greg Freemyer <greg DOT freemyer AT gmail DOT com>
Date: Thu, 31 Mar 2016 16:48:34 -0400
Message-ID: <CAGpXXZJV-nsB=xyO7=EBUb-JCk5KqMPS=bvg2aWgw_jm4OZFsQ@mail.gmail.com>
Subject: rsync performance degradation? Could be a windows issue?
To: cygwin AT cygwin DOT com
Content-Type: text/plain; charset=UTF-8

All,

I'm not sure this is on-topic, but at least I'm in cygwin when I
notice the below:

I do a lot of large data transfers between USB drives.  Often I get
great speeds (70MB/sec or more).

Sometimes it falls way off to closer to 20MB/sec with the same class
of hardware.

I experienced the "slow" transfer speed today, so I thought I'd ask if
anyone knew a way to resolve it?

The PC I'm running on is spec'ed for data processing so a 6 core (12
thread) setup with 128GB or RAM.

No significant data processing is going on.  Basically the machine is
currently dedicated to running rsync (as below).

I have 2 USB drives hooked up.  Both are USB-3 and should be able to
do 70MB/sec with no issue.

Neither drive has any unrelated I/O going on that I know of.  (I don't
see any in the Windows Performance Monitor.)

I have a folder with almost 200 4GB files ( 750GB total and all the
files are large).

I'm using "rsync -av" to copy files from the source to the destination
and the folder on the destination started out empty

Using Windows "Resource Monitor" I normally would see both drives
hitting over 70 MB/sec.  Today I'm seeing the source drive jump all
the way up to 125 MB/sec or so, but the destination is down around 20
MB/sec

When the 4GB source file completes reading, the source drive basically
goes idle for a while until the file is written out.

Then the source drive jumps back to 125 MB/sec until it finishes
reading the next file.  The destination drive on the other hand is
stuck down around 20 MB/sec.

I really don't think this is caused by slow hardware.  Could the
destination drive be dropping down to USB-2 mode?

===
And now that I've written up the above, the system has returned to a
more normal 75 MB/sec consistently on the output drive.

I'm still curious what might be going on.  As I say I move a lot of
data around as part of my work, and much of the time it is big groups
of either 1.5GB or 4GB files.

Thanks
Greg
--
Greg Freemyer
www.IntelligentAvatar.net

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