Hi,
Am trying to optimize the disk I/O performance for KVM guests running on
my SmartOS Host (RAID 10 with 4 disks), 8 physical cores, 100G+ RAM.
Running this command: time sh -c "dd if=/dev/zero of=ddfile bs=8k
count=250000 && sync"; rm ddfile
On the Host gives:
real 0m16.051s
user 0m0.186s
sys 0m3.181s
On a Centos guest gives:
real 0m43.182s
user 0m0.032s
sys 0m1.505s
- More than 50% degradation on write throughput performance. Been
surfing through many sites, and some suggest using io=native and cache=none
as qemu options to eliminate double caching etc. However, I can't seem to
find a way to do this. Tried editing the startvm file at /zones/{$UUID}/root
at the option. This is also true of any other image I am running where the
guest io performance is a far cry from the host performance.
"-drive" "file=/dev/zvol/rdsk
/zones/d0a2fc0f-e623-4423-bcba-b73a56d73c18-disk0,if=virtio,index=0,media=di
sk,boot=on" by adding io=native,cache=none to the option, but this file gets
overwritten every time the VM is restarted. Tried putting updating a VM with
these parameters also for the disk, but would not accept this. I know there
is an option called qemu_extra_opts, but don't think the syntax would be
right. BTW the Centos image above is an image downloaded from Joyent public
images.
The setting "echo zfs_vdev_max_pending/W0t35 | mdb -kw" seemed to give some
improvement on 1 server, but not on another host.
Any help on this would be much appreciated.
Thanks,
Gavin
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