[ubuntu] Disk Performance with KVM: IDE vs. VIRTIO

      Hi,

we just bought a new server: 2 Quadcore XEON, 6G RAM, 1T Soft-RAID1 HD on SATA, which I set up with Ubuntu 9.04 and KVM.

To find out the perfect setup for the KVM guests, I did some HD benchmarking with bonnie++. For that purpose I set up a minimum Ubuntu 9.04 guest with 2 additional LVM VGs as virtual drives: 1 IDE (sda), 1 VIRTIO (vda). The guest has 1 VCPU and only 100MB RAM.

Inside the guest I created an ext3 partition in each of the two additonal drives and mount them into 2 dirs: ~/ide and ~/virtio.

Now I run the bonnie++ drive test on the 2 dirs with 500MB files (so that it's much larger then the available RAM). Below are the results:

============ IDE ============
Version 1.03c ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
virtiotest 500M 28462 66 29208 7 34808 9 56499 85 362458 59 3791 13
------Sequential Create------ --------Random Create--------
-Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
virtiotest,500M,28462,66,29208,7,34808,9,56499,85, 362458,59,3790.7,13,16,+++++,+++,+++++,+++,+++++,+ ++,+++++,+++,+++++,+++,+++++,+++



============ VIRTIO ============
Version 1.03c ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
virtiotest 500M 27075 63 27448 7 50246 11 62734 79 243664 34 3124 57
------Sequential Create------ --------Random Create--------
-Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
virtiotest,500M,27075,63,27448,7,50246,11,62734,79 ,243664,34,3123.7,57,16,+++++,+++,+++++,+++,+++++, +++,+++++,+++,+++++,+++,+++++,+++

============ HOST SYSTEM ============
Version 1.03c ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
eve 11760M 65971 91 86969 24 42273 7 38865 71 91063 8 451.1 0
------Sequential Create------ --------Random Create--------
-Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
eve,11760M,65971,91,86969,24,42273,7,38865,71,9106 3,8,451.1,0,16,+++++,+++,+++++,+++,+++++,+++,+++++ ,+++,+++++,+++,+++++,+++

There are 2 things I dislike / don't understand:
- the performance on the disk via IDE emulation is not much different from the VIRTIO drivers. documentation says it should be a lot different
- the performance on both drives is approximatly only 1/3 to 1/2 of the performance on the HOST System. according the the docs, it should be almost the same VIRTIO and the HOST System

Can anybody please tell about his experiences with VIRTIO / KVM and/or comment my results.

Thanks,
Matthias