Re: I/O Wait on exportfs

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Jan 17, 2012 at 04:43:19PM +0100, Bertrand Jacquin wrote:
> Le mardi 17 janvier 2012 à 16h09, « J. Bruce Fields » a écrit :
> > On Tue, Jan 17, 2012 at 03:29:45PM +0100, Bertrand Jacquin wrote:
> > > For a specific case I have /etc/exports with 1281 entries as I need
> > > mount --bind to be exported to NFS Clients too.
> > 
> > Could you explain what you mean by that?
> 
> In this case, I need /srv/mail to be exported to clients. But for a 1
> month period, I need folders present in /srv/mail2 to be accessible in
> /srv/mail.
> 
> We are moving datas to a SAN, and to avoid modifying any mail configuration
> (and the long list depending on it), I mount /srv/mail2 subdirectory to
> /srv/mailsubdirectory until all subdirectory are migrated :
> 
>  # mount /dev/drbd5 /srv/mail
>  # mount /dev/mapper/iqn.dXX:san1.target0-lun0 /srv/mail2
>  # <moving data from /srv/mail/user1 to /srv/mail2/user1>
>  # mount --bind /srv/mail2/user1 /srv/mail/user1
> 
> To make /srv/mail2/user1 data visible for NFS client, I need to use
> crossmnt options in /etc/exports as nohide is client per client.
> 
> exports(5) say :
> 
>   Thus when a child filesystem "B" is mounted on a parent "A", setting
> 	crossmnt on "A" has the same effect as setting "nohide" on B.
> 
> But I can't say that this had work at all, but adding child filesystem
> in /etc/export, then 'mount -o remount' NFS partition on client fix
> that. I'm maybe wrong, but my tests put me in that way.

That's a bug, it should be enough just to export /srv/mail, and the
mounts underneath should then automatically be exported.

Hm--there have been a couple fixes in that area recently.  You might try
building the most recent nfs-utils.

Then you shouldn't need to list every subexport explicitly in
/etc/exports.

(That may not solve your performance problem, though.)

--b.

> 
> > > Since I have ~1100 entries, reexporting /etc/exports have some bad
> > > effects to connected clients, load rise to ~500 for 4/5 minutes, this is
> > > always reproducible.
> > > 
> > > This was using 'exportfs -ra'. I did try with 'exportfs
> > > 192.168.0.1:/srv/mail/1234' to avoid reexport every directories, and
> > > the sync process but the result is the same.
> > 
> > Does a -t option (see rpc.mountd(8)) help?
> 
> This is interesting
> 
> Bertrand
> 
> -- 
> Bertrand Jacquin, EXOSEC (http://www.exosec.fr/)
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