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DescriptionOrion Poplawski
2011-09-07 20:44:07 UTC
Description of problem:
I've had to disable raid-check because the check/resync process absolutely kills performance. Server is used for backups and for multiple kvm guests so a fair amount of IO.
Version-Release number of selected component (if applicable):
2.6.32-131.12.1.el6.x86_64
mdadm-3.2.2-1.el6.2.x86_64
Comment 3RHEL Program Management
2011-10-07 15:47:43 UTC
Since RHEL 6.2 External Beta has begun, and this bug remains
unresolved, it has been rejected as it is not proposed as
exception or blocker.
Red Hat invites you to ask your support representative to
propose this request, if appropriate and relevant, in the
next release of Red Hat Enterprise Linux.
It seems to be the combination of kvm guests and the raid10 resync that kills IO performance for some reason. Stopping all kvm guests during the resync (or stopping the resync if it is just a check) gets me back to >100MB/s read/write performance.
The kvm guests are using raw lvm volumes on a volume group on the raid10 array and using virtio. One kvm guest in particular that triggers it is a 2 cpu Fedora 14 instance running zabbix-server - so a fairly steady cpu and io load.
2.6.32-131.17.1.el6.x86_64
I just noticed that a copy between two disks on the host was crawling (5-10MB/s). I starting shutting down kvm guests (which were mainly idle) and now I'm up to 50-70MB/s. Something about kvm guests is really killing the host IO performance.
Any chance that having hyperthreading enabled would have any effect on this? I may disable just to see.