Hi. I have performance problems with IBM DB2 10.5 server on KVM guest: [db2inst1@wc8ws-auth ~]$ time db2 create db test DB20000I The CREATE DATABASE command completed successfully. real 7m46.155s user 0m0.022s sys 0m0.027s It takes 30 seconds to create a database on an image mounted with -oloop. I think it's because db2 uses O_DIRECT to ensure consistency. I also think that O_DIRECT is not propagated to host with default cache modes in VM settings. The real problem is: when guest writes data in small blocks, host CPU becomes a bottleneck. I hava a relatively old 24-core Xeon. Host `top` shows 130% CPU usage by qemu-kvm, when I run the following command: [root@wc8ws-auth ~]# </dev/zero timeout -sINT 30s dd iflag=fullblock oflag=direct conv=notrunc of=./bigfile bs=8192 140384+0 records in 140384+0 records out 1150025728 bytes (1.2 GB) copied, 29.9992 s, 38.3 MB/s I tried all buses, cache modes and IO modes; "Cache mode=none" is slower, others are almost equal. I moved from image file to LVM. This raised the speed from 16M to 38M. I also tried VirtualBox, but it's neither faster, nor slower, and it eats CPU too. -- -------------------------------------------------------------------------------- Kind regards, Ilya Basin software engineer Reksoft Skype: basin_ilya phone +7(812)324-24-40*553