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Re: [Qemu-discuss] virtual disks perfermonca <=2MB/s

From: Vincenzo Romano
Subject: Re: [Qemu-discuss] virtual disks perfermonca <=2MB/s
Date: Mon, 20 Feb 2017 12:13:29 +0100


I could be wrong, but are you willing to run a VM with a disk image
If not, why are you quoting your network throughput?

Could you please try (on a separate test VM) raw and qcow2?
In understand your concerns about the disk space allocation, but if
you create a virtual disk of 50GB, I think you'd know it could grow up
to that size and that it won't automatically shrink back.

Please, elaborate more on your environment and objectives.

Vincenzo Romano - NotOrAnd.IT
Information Technologies

2017-02-20 12:05 GMT+01:00 Mimiko <address@hidden>:
> Hello.
> I've setup qemu / kvm on Debian Wheezy to host some Debian Jessie guests.
> I create disk like this:
> virsh vol-create-as --pool default --name root.vhd --capacity 50G --format
> vpc
> Then create a virtual with this:
> virt-install --connect qemu:///system \
> --ram 2048 \
> --vcpus=4 \
> --cpuset=auto \
> --pxe \
> --os-type linux \
> --boot network,hd,menu=on \
> --disk vol=default/root.vhd,device=disk,bus=virtio,cache=writethrough \
> --network=bridge:br0,model=virtio \
> --noautoconsole \
> --hvm \
> --autostart \
> --check-cpu
> After setting up the system I've got poor disk performance.
> Using
> time dd if=/dev/zero of=/tmp/test oflag=direct bs=64k count=16000
> I get 1048576000 bytes (1.0 GB) copied, 397.473 s, 2.6 MB/s
> I've changed cache to writeback and got 20MB/s with this test. But copying a
> file to this virtual using samba gives me no more of 2 MB/s.
> I've tested network connectivity with iperf and got around 750Mbit/s, which
> I think is satisfactory.
> I will not want to use raw devices, as it is not self expanded and will use
> whole space regardless of how much real data occupy.
> libvirtd (libvirt)
> Is there a way to increase disk speed to at least 50MB/s ?

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