# xen 4 image disk qemu-dm disk write brutal slow

## chalan

hi. i have a big problem, messing around over 1week with no success and asking for help. i have a fresh install x86_64 gentoo 3.4.2-hardened-r1 kernel and profile dom0 running on raid10 mdadm and lvm with xen-4.1.2 and xen-tools-4.1.2-r3 compiled with qemu and hvm. domU is PV gentoo. domU disk write is max 500kBs which is unusable. tap:aio or file in the config is the same result... when i make partiton in lvm and use phy: in config everything is OK, but i need the domU to run on disk image so tap:aio. is there any limitation in kerner or xen qemu? when its write 500kBs showing 100% which means like it is somewhere set to max 500kBs?

iotop under dom0 show:

17655 be/4 root 0.00 B/s 478.62 K/s 0.00 % 99.43 % qemu-dm -d 2 -domain-name kronos -nographic -M xenpv

i was using old xen 3 with tap:aio with no problem. plese help me and sorry for my english...

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