[Users] Horrid performance during disk I/O

[Andrew Cathrow]

----- Original Message -----
> From: "Blaster" <blaster at 556nato.com>
> To: users at ovirt.org
> Sent: Monday, January 13, 2014 12:22:37 PM
> Subject: [Users] Horrid performance during disk I/O
> 
> 
> This probably more appropriate for the qemu users mailing list, but
> that list doesn’t get much traffic and most posts go unanswered…
> 
> As I’ve mentioned in the past, I’m migrating my environment from ESXi
> to oVirt AIO.
> 
> Under ESXi I was pretty happy with the disk performance, and noticed
> very little difference from bare metal to HV.
> 
> Under oVirt/QEMU/KVM, not so much….
> 
> Running hdparm on the disk from the HV and from the guest yields the
> same number, about 180MB/sec (SATA III disks, 7200RPM).  The problem
> is, during disk activity, and it doesn’t matter if it’s Windows 7
> guests or Fedora 20 (both using virtio-scsi) the qemu-system-x86
> process starts consuming 100% of the hypervisor CPU.  Hypervisor is
> a Core i7 950 with 24GB of RAM.  There’s 2 Fedora 20 guests and 2
> Windows 7 guests.  Each configured with 4 GB of guaranteed RAM.
> 

Did you compare virtio-block to virto-scsi, the former will likely outperform the latter.


> Load averages can go up over 40 during sustained disk IO.
>  Performance obviously suffers greatly.
> 
> I have tried all combinations of having the guests on EXT 4, BTRFS
> and using EXT 4 and BTRFS inside the guests, as well as direct LUN.
>  Doesn’t make any difference.  Disk IO sends qemu-system-x86 to high
> CPU percentages.
> 
> This can’t be normal, so I’m wondering what I’ve done wrong.  Is
> there some magic setting I’m missing?
> 
> 
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>