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...tpoint (with sync). The local filesystem sits on top of an md software RAID of SATA HDDs. I have read some conflicting information about which cache option is used by default. This documentation states that cache=writethrough is the default: http://www-01.ibm.com/support/knowledgecenter/linuxonibm/liaat/liaatbpkvmguestcache.htm?lang=en However this SuSE documentation claims that QEMU 1.2.x and newer allows the driver to select which cache mode, and it often defaults to cache=writeback: https://www.suse.com/documentation/sles11/book_kvm/data/sect1_1_chapter_book_kvm.html Which is correct? How is...

...ocal filesystem sits on top of an md software RAID of SATA HDDs. > > I have read some conflicting information about which cache option is > used by default. This documentation states that cache=writethrough is > the default: > http://www-01.ibm.com/support/knowledgecenter/linuxonibm/liaat/liaatbpkvmguestcache.htm?lang=en The above sounds incorrect (refer below). > However this SuSE documentation claims that QEMU 1.2.x and newer > allows the driver to select which cache mode, and it often defaults to > cache=writeback: > https://www.suse.com/documentation/sles11/book_kv...

Hi, I have a strange phenomenon that I cannot readily explain so I wonder if anyone here can shed a light on this. The host system is a Dell r815 with 64 cores and 256G ram and has centos 6 installed. The five guests are also running centos 6 and are running as a hadoop cluster. The problem is that I see disk-io spikes in the vm's which then cause soft lockups in the guest but I also see

Hi all, I'm running a VM using libvirt+KVM and I have a disk performance issue. The host is the following: 4 cores Intel Xeon 5140@2.33 GHz, 16 GB of RAM, SATA HDD, OS Debian Wheezy, libvirt 0.9.12-11, QEMU-KVM 1.1.2+dfsg-2. The guest: 1 CPU, 2 GB RAM running Debian 7.0, image in compressed qcow2 format. When I try do run "dd if=/dev/zero of=io.test bs=32768k count=40" I get