Joris van Lieshout created CLOUDSTACK-7319:
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Summary: Copy Snapshot command to heavy on XenServer Dom0
resources when using dd to copy incremental snapshots
Key: CLOUDSTACK-7319
URL: https://issues.apache.org/jira/browse/CLOUDSTACK-7319
Project: CloudStack
Issue Type: Bug
Security Level: Public (Anyone can view this level - this is the default.)
Components: Snapshot, XenServer
Affects Versions: 4.2.0, 4.1.0, 4.0.2, 4.0.1, 4.0.0, 4.1.1, Future, 4.2.1,
4.3.0, 4.4.0, 4.5.0, 4.3.1, 4.4.1
Reporter: Joris van Lieshout
Priority: Critical
We noticed that the dd process was way to agressive on Dom0 causing all kinds
of problems on a xenserver with medium workloads.
ACS uses the dd command to copy incremental snapshots to secondary storage.
This process is to heavy on Dom0 resources and even impacts DomU performance,
and can even lead to domain freezes (including Dom0) of more then a minute.
We've found that this is because the Dom0 kernel caches the read and write
operations of dd.
We've developed a patch on the xenserver scripts
/etc/xapi.d/plugins/vmopsSnapshot that added the direct flag of both input and
output files.
Our test have shown that Dom0 load during snapshot copy is way lower. I will
upload the patch on review.
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