What does ZFS write when nothing should write there?
Dmitry Morozovsky
marck at rinet.ru
Fri Jan 10 13:29:24 UTC 2014
On Fri, 10 Jan 2014, Steven Hartland wrote:
> > > > I've created 6 zpools, each of them with zpool create -m /data/A dataA
> > > > mirror
> > > > daX daY.
> > > > The machine has nothing running except sshd and my shell.
> > > >
> > > > Yet, I see this in gstat:
> > > [snip]
> > >
> > > > 0 88 0 0 0.0 82 573 4.1 9.0 da5
> > > > 0 89 0 0 0.0 83 573 4.8 9.8 da6
> > > > 0 87 0 0 0.0 81 573 2.6 5.7 da9
> > > > 0 89 0 0 0.0 84 573 3.0 6.7 da10
> > > Did you turn off atime?
> > >
> > No, but how does it matter?
> > The process list is the following: init, getty, sshd, csh and the pool is
> > completely empty.
>
> With atime on each time you access a file it will update its "atime"
> hence causing writes.
>
> We use atime=off at the pool level on all machines to avoid that
> zfs set atime=off <pool>
BTW, it seems that ZFS updates atime of some inodes (root one?) on every kernel
update thread invocation even when completely empty -- is it correct behaviour?
--
Sincerely,
D.Marck [DM5020, MCK-RIPE, DM3-RIPN]
[ FreeBSD committer: marck at FreeBSD.org ]
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*** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- marck at rinet.ru ***
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