Changing scsi controller type increases disk write but also increases server load!

Hello all,

Been running some raid test the last few months and the findings are somewhat amusing and scary at the same time, not sure if its a bug but we need some help to find out the issues and solution.

Example of the vm config

bootdisk: scsi0
cores: 4
memory: 4096
name: test
ostype: l26
scsi0: SATA:100/vm-100-disk-1.raw,format=raw,cache=writeback,size=40G
scsihw: megasas
sockets: 1

results 17G copied at 41.5671s, 413 MB/s and server load will go to 10-14 load average

running this command in the vm dd if=/dev/zero of=test bs=1M count=16k conv=fdatasync The vm and host schedulers set to deadline changing to noop shows a slight difference but not enough to post the results.

bootdisk: scsi0
cores: 4
ide2: local:iso/CentOS-6.4-x86_64-minimal.iso,media=cdrom
memory: 4096
name: test
ostype: l26
scsi0: SATA:100/vm-100-disk-1.raw,format=raw,cache=writeback,size=40G
scsihw: lsi
sockets: 1

results 17G copied at 116.105s, 148 MB/s and server load will go to 3 to 4 load average

Just changing the controller type for the vm to lsi which is set by default gives me slower disk speeds but the load of the system doesn't go past 4-5 and the io delay is not as high.



bootdisk: scsi0
cores: 4
ide2: local:iso/CentOS-6.4-x86_64-minimal.iso,media=cdrom
memory: 4096
name: test
ostype: l26
scsi0: SATA:100/vm-100-disk-1.raw,format=raw,cache=writeback,size=40G
scsihw: virtio-scsi-pci
sockets: 1

using virto for the controller type has the system load going to 50+ and shows the disk response as 17G copied at 113.133s, 152 MB/s

root@host-03:~# pveperf
CPU BOGOMIPS: 72531.28
REGEX/SECOND: 930624
HD SIZE: 94.49 GB (/dev/mapper/pve-root)
BUFFERED READS: 505.01 MB/sec
AVERAGE SEEK TIME: 0.15 ms
FSYNCS/SECOND: 2384.59
DNS EXT: 74.14 ms
DNS INT: 58.48 ms (google.com)


The raid card used is a lsi megaraid sas 9260-8I latest firmware.

Thanks in advance.