Thanks a lot for your reply and sorry for my double post out of impatientness.
> > I then startet a fedora 22 live system and I saw the same problem. It > > happens > > on both the ramdisk and a ext4 filesystem. > > "it" == qemu-img map hangs or takes a very long time? I never waited for it to complete but I guess it just takes very long. > > Can you post a shell script that reproduces this with a ramdisk? That > seems like the easiest way to get people debugging it. You can use the following commands. mkfs.ext4 /dev/ram0 mkdir -p /mnt/tmp mount /dev/ram0 /mnt/tmp cd /mnt/tmp qemu-img create test 500G time qemu-img map test This takes foreover on all my systems. Running everything on tmpfs instead is fast mkdir -p /mnt/tmp mount -t tmpfs -o size=1G none /mnt/tmp cd /mnt/tmp qemu-img create test 500G time qemu-img map test I did run a few more tests on different systems and made an interessting observation. lseek is damn slow if the blockdevice has an I/O size of 512 bytes (like the raid controller of my server or a ramdisk) and runs fast with 4096 bytes (like the ssd of my workstation or tmpfs). I confirmned this also with with a few other drives but it still could be coincidence... You can check the I/O size by running fdisk <dev> p Cheers, David To: stefa...@gmail.com Cc: qemu-devel@nongnu.org
