3:07 p.m.
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Von: Stefan Wendler [stefan.wendler(a)tngtech.com]=0A=
Gesendet: Montag, 27. Oktober 2014 11:39=0A=
An: Markus Stockhausen=0A=
Cc: users(a)ovirt.org=0A=
Betreff: Re: [ovirt-users] Deleting large snapshots blocks the whole clus=
ter=0A=
=0A=
Hi,=0A=
=0A=
do you mean during snapshot deletion or in general?=0A=
=0A=
In general we do not have any swap usage at all. On none of the 4 hosts.=
=0A=
=0A=
We had some swap I/O on the host that is SPM most of the time. But not=0A=
during that period where we tried to delete the snapshot.=0A=
=0A=
=0A=
I thought of the bug described in RH bugzilla 1138690 "[SCALE] snapshot del=
etion -> =0A=
heavy swapping on SPM". In case you have no access to it (as it is RHEV tag=
ged): =0A=
=0A=
qemu-img reads through pagecache during snapshot deletion. A new flag has b=
een =0A=
intrduced in August this year that allows to avoid page cache. This flag mu=
st be=0A=
provided by OVirt/RHEV. Target release is 3.6. =0A=
=0A=
Until then the only bugfix is to drop pagecache manually on regular interva=
ls on the =0A=
hypversior and especially the SPM node.=0A=
=0A=
Markus=0A=
=0A=
=0A=
Cheers,=0A=
Stefan=0A=
=0A=
On 10/27/14 11:08, Markus Stockhausen wrote:=0A=
> Do you see swapping on the SPM? If yes a regular echo 3 > drop_caches c=
ould help.=0A=
>=0A=
> Markus=0A=
>=0A=
> Am 27.10.2014 10:57 schrieb Stefan Wendler <stefan.wendler(a)tngtech.com>=
:=0A=
> Hi,=0A=
>=0A=
> we have some really large snapshots left from a migration. Since our=0A=
> store is almost full now we have to delete them now.=0A=
>=0A=
> Some snapshots are around 1TB already.=0A=
>=0A=
> The last time we tried to delete a ~500GB snapshot the delete task=0A=
blocked the whole diskstore's IO and the whole cluster and all hosts=0A=
became unavailable.=0A=
=0A=
Is there a way to delete large snapshots in a "humane" way that will not=
=0A=
block everything?=0A=
=0A=
Cheers,=0A=
Stefan=0A=
=0A=
=0A=
=0A=
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