top io mode

Kostik Belousov kostikbel at
Thu Nov 25 22:45:00 UTC 2010

On Thu, Nov 25, 2010 at 04:35:53PM -0600, Adam Vande More wrote:
> On Thu, Nov 25, 2010 at 3:04 PM, Jeremy Chadwick
> <freebsd at>wrote:
> > Bad form to follow up to my own Email of course, but some discussion
> > material:
> >
> I'm a frequent offender myself so I won't be pointing any fingers.
> "top -m io" doesn't show any I/O writes, while gstat(8) does, and to
> > numerous devices all which make up some form of ZFS pool.
> >
> Yes, it's a generic ZFS mirror.
> If you do something like "dd if=/dev/urandom of=/pool/file bs=64k", does
> > "top -m io" show write I/O for the "dd" process?
> >
> It does not on my ZFS STABLE system with Kostick's path.  So the patch fixes
> reads, but not writes. cc'ing to notify in case he has more ideas.
Can you show exact command and describe some details about setup for
the case where you still do not observe the counter in top ?
(With my patch applied).

There are two mixed things in the thread:
First, there is (was) a missed accounting for i/o to physical devices,
and the patch I posted should fix it.

Second, it is relatively well-known that ZFS does not properly accounts
i/o. Might be, the patch by Andrew fixes it, I do not know.
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