From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mikulas Patocka <mpatocka@redhat.com>
Subject: Re: [PATCH 1/2] dm-kcopyd: introduce per-module throttle
 structure
Date: Tue, 7 Jun 2011 13:50:16 -0400 (EDT)
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To: device-mapper development <dm-devel@redhat.com>, Joe Thornber <thornber@redhat.com>
Cc: "Alasdair G. Kergon" <agk@redhat.com>
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On Fri, 3 Jun 2011, Joe Thornber wrote:

> On Thu, Jun 02, 2011 at 03:55:16PM -0400, Mikulas Patocka wrote:
> > > iv) you haven't explained how the sys admin works out the correct
> > > throttle value.
> > 
> > There is no "correct" value. The "correct" value depends on how important 
> > is copying itself v.s. other i/o.
> 
> So who is going to set this?  Do you really have no advice for them
> beyond 'there is no correct value'?

I did some tests. I did some random and sequential I/O on the same disk 
while mirror was resynchronizing. The result is this:

random read:
mirror throttle / IOs per second
100%	94
75%	113
50%	127
25%	145
idle	160

sequential read:
mirror throttle / throughput MB/s
100%	104
75%	118
50%	122
25%	127
idle	134

Mikulas