On Fri, Oct 23, 2015 at 6:55 AM, Julian De Marchi <julian@jdcomputers.com.au> wrote:
heya--

Playing around with oVirt 3.6 on some new kit before I rack and stack in the DC.

  - Dell Eql PS4210(Raid-6)
  - Dell R630
  - Dell N400 10GB switch

I have my 10GB interfaces bonded and in a port-channel. I have setup a basic 3.6 oVirt self-hosted stack.

I am seeing some pretty big differences in disks speeds from the self-hosted engine and a VM guest. Both are direct luns via iscsi from the SAN on the 10GB port-channel. Normal network traffic does not go over the 10GB.

On the engine I'm seeing this:

# dd if=/dev/zero of=~/testfile bs=1G count=1 oflag=dsync

You are not using direct IO, please add relevant flag.
 
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB) copied, 1.58877 s, 676 MB/s

On a test VM I'm seeing this:

# dd if=/dev/zero of=~/testfile bs=1G count=1 oflag=dsync
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB) copied, 22.0732 s, 48.6 MB/s

I have played with the disk drivers for my guest VM, changing between drivers does not change the speed at all.

I assume both VMs have the same image format and drivers?
 

What ideas do you folks have for me to narrow down this slow down? I don't really know where to start with this one. I also noticed that 3.6 does not yet have ovirt-guest-agent available.

I know DD is not the best test for disk speeds, but it works for what I need right now, iozone will be next when I'm happy.

dd is by no means a tool for disk speeds. Specially not when you are writing zero's. I suggest fio .
Y.
 

Many thanks!

--julian
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