People should be aware that cache=writeback should only be used if you
do not care about the very real possibility of guest disk corruption
should the guest or host fail unexpectedly. Given that there is no
facility for shutting down guests cleanly on host shutdown one should be
very wary of
Thanks müzso, this worked for me (kvm, ubuntu, xp 32 guest).
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https://bugs.launchpad.net/bugs/550409
Title:
Slow disk IO for all guests with all disc modes and types.
** Changed in: libvirt (Ubuntu)
Status: Incomplete = Confirmed
--
Slow disk IO for all guests with all disc modes and types.
https://bugs.launchpad.net/bugs/550409
You received this bug notification because you are a member of Ubuntu
Server Team, which is subscribed to libvirt in ubuntu.
I can confirm Fabian's tip about the cache=writeback tip. I've one more
tip for you: if you are using image files for virtual disks, then using
ext3 as the filesystem for the host OS will greatly improve the disk I/O
of your guest operating systems. With a Lucid+ext4+KVM+WindowsXP guest
** Tags added: cache ext3 ext4 libvirt qemu writeback
** Tags removed: amd64 apport-bug
--
Slow disk IO for all guests with all disc modes and types.
https://bugs.launchpad.net/bugs/550409
You received this bug notification because you are a member of Ubuntu
Server Team, which is subscribed to
I've tested this with Karmic+KVM+ext4 and the problem is present as
well. Using Karmic+KVM+ext3 resulted in the same performance boost as on
Lucid.
I'd be nice if others could comment on whether this problem is present
with Lucid/Karmic+Xen+ext4 too. I guess it should be, because the
problem
I forgot to add: the cache policy is a QEMU thing and since Xen uses
QEMU too, it should be affected as well.
--
Slow disk IO for all guests with all disc modes and types.
https://bugs.launchpad.net/bugs/550409
You received this bug notification because you are a member of Ubuntu
Server Team,
With the cache=writeback in a Lucid+KVM+libvirt+WindowXP guest setup
I've experienced near host-level I/O performance in the guest. Thus this
makes use of a virtio driver unnecessary.
Btw. for casual libvirt users ... adding the cache=writeback option means:
1. stop the VM (in case it's running)
If you want to read more about QEMU disk cache internals, I've found a short
presentation on the topic here:
The KVM/qemu storage stack (by Christoph Hellwig)
www.linuxfoundation.jp/jp_uploads/JLS2009/jls09_hellwig.pdf
--
Slow disk IO for all guests with all disc modes and types.
I want to start kvm without libvirt and with additional -drive options.
Can someone please guide me for how I can avoid libvirt?
--
Slow disk IO for all guests with all disc modes and types.
https://bugs.launchpad.net/bugs/550409
You received this bug notification because you are a member of
Successfully started kvm without libvirt and with additional -drive options:
cache=writeback,aio=native
Copied 1,3GB to windows guest share over GB network with 41MB/s sustained
transfer rate.
Windows and linux Guests are running very smooth again.
Maybe libvirt should use those -drive
I second this - just incredibly slow I/O results in nearly unusable KVM guests.
Tested with lucid guests and windows 7 using virtio drivers.
I am using a luks crypted lvm partition on top of a sata md raid.
Changing I/O schedulers doesn´t help.
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Slow disk IO for all guests with all disc
I also just ran IOmeter on the Windows guest again, against both IDE and
SCSI emulation, against guest discs hosted on the mdraid5 with lvm, as well
as a single SATA2 7500RPM disc. Identical results against both targets.
4096B blocks = 0.75MBps. 16KB blocks = 1.0MBps, 32KB blocks = 4MBps, =64KB
Could you describe which commands you've used to:
1. create the guests
2. start the guests
3. run the benchmarks
** Changed in: libvirt (Ubuntu)
Status: New = Incomplete
** Changed in: libvirt (Ubuntu)
Importance: Undecided = Low
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Slow disk IO for all guests with all disc
1. create the guests
The first set of guests I created (both Windows and Linux) were created with
virt-manager. I used default settings for both Windows and Linux guests.
Windows guests defaulted to IDE emulation, and Linux guests defaulted to Virtio
emulation. I have since tried all
On Tue, Mar 30, 2010 at 03:42:56PM -, Ben Selinger wrote:
2. start the guests
Guests are normally started with virt-manager, which results in the following
command:
/usr/bin/kvm -S -M pc-0.12 -cpu qemu32 -enable-kvm -m 512 -smp 1 -name winxp
-uuid eb0416e2-54d2-d4cb-936d-331edbe443c0
This is the command used to start one of the affect Linux guests:
/usr/bin/kvm -S -M pc-0.12 -enable-kvm -m 512 -smp 1 -name ubuntu -uuid
9de5914b-f448-cb8d-066f-ec51286c80c0 -chardev
socket,id=monitor,path=/var/lib/libvirt/qemu/ubuntu.monitor,server,nowait
-monitor chardev:monitor -boot c -drive
** Attachment added: Dependencies.txt
http://launchpadlibrarian.net/42298604/Dependencies.txt
--
Slow disk IO for all guests with all disc modes and types.
https://bugs.launchpad.net/bugs/550409
You received this bug notification because you are a member of Ubuntu
Server Team, which is
** Description changed:
- Very slow disk throughput for all guest OS's. Windows seems to be the
slowest at ~3MBps. Linux guests usually get ~18MBps. All tests performed on
two physical hosts.
+ Very slow disk throughput for all guest OS's. Windows seems to be the
slowest at ~3MBps.
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