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.
The disks are preallocated
Now I have 3 processes of kind: /usr/bin/qemu-img convert -p -t none -T none -f raw /rhev/data-center/59b7af54-0155-01c2-0248-000000000195/fad05d79-254d-4f40-8201-360757128ede/images/8f62600a-057d-4d59-9655-631f080a73f6/21a8812f-6a89-4015-a79e-150d7e202450 -O raw /rhev/data-center/mnt/blockSD/6911716c-aa99-4750-a7fe-f83675a2d676/images/c3973d1b-a168-4ec5-8c1a-630cfc4b66c4/27980581-5935-4b23-989a-4811f80956ca
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.
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