Awful FreeBSD 9 block IO performance in KVM

[Wojciech Puchar]

> You are right. It is not capped at that speed:
>
> root at freebsd:/root # dd if=/dev/zero of=/dev/da1 bs=16384 count=262144
>
>
>
> 262144+0 records in
> 262144+0 records out
> 4294967296 bytes transferred in 615.840721 secs (6974153 bytes/sec)
>
>
you did test da1 while dmesg are about da0?

is it OK and da1 is another qemu-kvm vdisk?

If so, check

dd if=/dev/zero of=/dev/da1 bs=512 count=256k

and compare speed.

i bet at something near 250kB/s and i think it is long I/O service 
pathlength in qemu-kvm SCSI device simulator.

Just my bet i don't run FreeBSD on any VM (as opposed to running Windows 
under FreeBSD in VBox)

check out how much CPU is used on the host side when you do that test.