On Thu, Sep 28, 2017 at 2:34 PM, Kevin Wolf <kwolf@redhat.com> wrote:
Am 28.09.2017 um 12:44 hat Nir Soffer geschrieben:
On Thu, Sep 28, 2017 at 12:03 PM Gianluca Cecchi < gianluca.cecchi@gmail.com> wrote:
Hello, I'm on 4.1.5 and I'm cloning a snapshot of a VM with 3 disks for a total of about 200Gb to copy The target I choose is on a different domain than the source one. They are both FC storage domains, with the source on SSD disks and the target on SAS disks.
[snip]
but despite capabilities it seems it is copying using very low system resources.
We run qemu-img convert (and other storage related commands) with:
nice -n 19 ionice -c 3 qemu-img ...
ionice should not have any effect unless you use the CFQ I/O scheduler.
The intent is to limit the effect of virtual machines.
Ah, ok. The hypervisor is ovirt node based on CentOS 7 so the default scheduler should be deadline if not customized in node. And in fact in /sys/block/sd*/queue/scheduler I see only [deadline] contents and also for dm-* block devices where it is not none, it is deadline too
I see this both using iotop and vmstat
vmstat 3 gives: ----io---- -system-- ------cpu----- bi bo in cs us sy id wa st 2527 698 3771 29394 1 0 89 10 0
us 94% also seems very high - maybe this hypervisor is overloaded with other workloads? wa 89% seems very high
The alignment in the table is a bit off, but us is 1%. The 94 you saw is part of cs=29394. A high percentage for wait is generally a good sign because that means that the system is busy with actual I/O work. Obviously, this I/O work is rather slow, but at least qemu-img is making requests to the kernel instead of doing other work, otherwise user would be much higher.
Kevin
Yes, probably a misalignement of output I truncated. Actually a sampling of about 300 lines (once every 3 seconds) shows these number of lines occurrences and related percentage user time 195 0% 95 1% So user time is indeed quite low wait time: 105 7% 58 8% 33 9% 21 6% 17 10% 16 5% 16% 12 11% 9 12% 7 14% 6 13% 2 15% 1 4% 1 16% 1 0% with wait time an average of 7% AT the end the overall performance in copying has been around 30MB/s that probably is to be expected do to how the qemu-img process is run. What about the events I reported instead? Gianluca