Re: [libvirt] [User question] Huge buffer size on KVM host

On Aug 15, 2012, at 2:57 PM, Avi Kivity wrote: >> >> We are using logical volumes and the cache is set to 'none'. > > Strange, that should work without any buffering. > > What the contents of > > /sys/block/sda/queue/hw_sector_size > > and > > /sys/block/sda/queue/logical_block_size > > ? > Hi Avi, It seems that the kernel on that particular machine is too old, those entries are not featured. We checked on a comparable setup with a newer kernel and both entries were set to 512. We also did have a third more thorough look on the caching. It turns out that the virt-manager does not seem to honor the caching adjusted in the GUI correctly. We disabled caching on all virtual devices for this particular VM and checking with "ps -fxal" revealed, that only one of those devices (and a rather small one too) had this set. We corrected this in the XML file directly and the buffer size currently resides at around 1.8 GB after rebooting the VM (the only virtio device not having the cache=none option set is now the (non-mounted) cdrom).