[ovirt-users] NFS IO timeout configuration

[Yaniv Kaul]

On Tue, Jan 12, 2016 at 10:45 PM, Markus Stockhausen <
stockhausen at collogia.de> wrote:

> >> Von: Yaniv Kaul [ykaul at redhat.com]
> >> Gesendet: Dienstag, 12. Januar 2016 13:15
> >> An: Markus Stockhausen
> >> Cc: users at ovirt.org; Mike Hildebrandt
> >> Betreff: Re: [ovirt-users] NFS IO timeout configuration
> >>
> >> On Tue, Jan 12, 2016 at 9:32 AM, Markus Stockhausen
> stockhausen at collogia.de> wrote:
> >> Hi there,
> >>
> >> we got a nasty situation yesterday in our OVirt 3.5.6 environment.
> >> We ran a LSM that failed during the cleanup operation. To be precise
> >> when the process deleted an image on the source NFS storage.
> >
> > Can you share with us your NFS server details?
> >Is the NFS connection healthy (can be seen with nfsstat)
> >Generally, delete on NFS should be a pretty quick operation.
> > Y.
>
> Hi Yaniv,
>
> we usually have no problems with our NFS server. From our observations we
> only have issues when deleting files with many extents. This applies to all
> OVirt images files. Several of them have more than 50.000 extents, a few
> even more than 300.000.
>
> > xfs_bmap 1cb5906f-65d8-4174-99b1-74f5b3cbc537
> ...
>         52976: [629122144..629130335]: 10986198592..10986206783
>         52977: [629130336..629130343]: 10986403456..10986403463
>         52978: [629130344..629138535]: 10986206792..10986214983
>         52979: [629138536..629138543]: 10986411656..10986411663
>         52980: [629138544..629145471]: 10986214992..10986221919
>         52981: [629145472..629145575]: 10809903560..10809903663
>         52982: [629145576..629145599]: 10737615056..10737615079
>
> Our XFS is mounted with:
>
> /dev/mapper/vg00-lvdata on /var/nas4 type xfs
> (rw,noatime,nodiratime,allocsize=16m)
>
> Why we use allocsize=16M? We once started with allocize=512MB. This
> led to sparse files that did not save much bytes. Because a single byte
> written
> resulted in a 512MB allocation. Thin allocation of these files resulted in
> long runtimes
> for formatting disks inside the VMS. So we reduced to 16MB as a balanced
> config
>
> This works quite well but not for remove operations.
>
> Better ideas?
>

Sounds like an XFS issue more than NFS.
I've consulted with one of our XFS gurus - here's his reply:

For vm image files, users should set up extent size hints to define
> the minimum extent allocation size in a file - allocsize does
> nothing for random writes into sparse files. I typically use a hint
> of 1MB for all my vm images....`
>

Y.


>
> Markus
>
>
>
>
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