Am 24.06.2014 um 09:25 hat lihuiba geschrieben:
> >Can you confirm that making L2_CACHE_SIZE much bigger solves the
> >problem?
> Yes, it is confirmed.
> When I run fio randread with a 7GB or 8GB size, result is close to that of
> raw image.
> But when the size is increased to 9GB, the result drop
On Mon, Jun 23, 2014 at 02:20:25PM +0800, lihuiba wrote:
> I think I have found the reason:
> There's a cache in qemu that accelerates the transform of virtual LBA to
> cluster offset of qcow2 image.
> The cache has a fixed size of 16x8192=128k in my configuration, which
> corresponds to a 8GB (1
On Mon, Jun 23, 2014 at 11:14:25AM +0800, lihuiba wrote:
> >Did you prefill the image? Amplification could come from cluster allocation.
> Yes!
> I forgot to mention that I created the qcow2 image with
> 'preallocation=metadata', and I have allocated
> the data blocks with dd in VM.
>
>
> Creat
I think I have found the reason:
There's a cache in qemu that accelerates the transform of virtual LBA to
cluster offset of qcow2 image.
The cache has a fixed size of 16x8192=128k in my configuration, which
corresponds to a 8GB (128K*64KB)
mapping size. So when the "working set" of fio exceeds 8G
Cc'ing more qcow2 experts.
On Mon, 06/23 11:14, lihuiba wrote:
> >Did you prefill the image? Amplification could come from cluster allocation.
> Yes!
> I forgot to mention that I created the qcow2 image with
> 'preallocation=metadata', and I have allocated
> the data blocks with dd in VM.
>
>
>Did you prefill the image? Amplification could come from cluster allocation.
Yes!
I forgot to mention that I created the qcow2 image with
'preallocation=metadata', and I have allocated
the data blocks with dd in VM.
Creating image in host:
qemu-img create -f qcow2 -preallocation=metadata test.
On Mon, 06/23 10:06, lihuiba wrote:
> Hi, all
>
>
> I'm using a qcow2 image stored on a SSD RAID1 (2 x intel S3500), and I'm
> benchmarking the
> system using fio. Although the throughput in VM (with KVM and virtio enabled)
> is acceptable (67%
> of thoughtput in host), the IOPS performance see
Hi, all
I'm using a qcow2 image stored on a SSD RAID1 (2 x intel S3500), and I'm
benchmarking the
system using fio. Although the throughput in VM (with KVM and virtio enabled)
is acceptable (67%
of thoughtput in host), the IOPS performance seems is extremely low only
2% of IOPS in host.
