Hello, I'm currently evaluating to switch our virtualization servers to a newer OS. This includes a switch from qemu 1.7 to 2.2 or 2.3. Our system heavily relies on big sparse images and drive_mirror. While testing, I experienced some problems with that combination. The strange thing is, that everything works flawlessly on my workstation but fails on my servers.
Testcase: # qemu-img create test 500G # time qemu-img map test Systems: O3-3: Kubuntu 15.04 Workstation with stock-kernel 3.19.0-18-generic and stock qemu 2.2.0 Dinah: Ubuntu Server 15.04 with stock-kernel 3.19.0-18-generic and stock qemu 2.2.0 Result on O3-3: root@o3-3:~# qemu-img create test 500G Formatting 'test', fmt=raw size=536870912000 root@o3-3:~# time qemu-img map test Offset Length Mapped to File real 0m0.049s user 0m0.048s sys 0m0.000s Result on dinah: root@dinah:~# qemu-img create test 500G Formatting 'test', fmt=raw size=536870912000 root@dinah:~# time qemu-img map test Offset Length Mapped to File ^C real 0m41.862s user 0m0.004s sys 0m0.068s (Stopped with ^C) Strace on O3-3: https://gist.github.com/anonymous/f221035e9176f7c71c74 Strace on dinah: https://gist.github.com/anonymous/40b42888a65478c90b32 A git bisect between 1.7 and master revealed 7c15903789953ead14a417882657d52dc0c19a24 "block/raw-posix: use seek_hole ahead of fiemap" as bad but this is not the real problem. I also tried to switch from btrfs to ext4 but it didn't change anything. At this point, I was pretty sure that was just stupit and missing something trivial. I then startet a fedora 22 live system and I saw the same problem. It happens on both the ramdisk and a ext4 filesystem. Any ideas on this? I'm pretty much stuck at this point. Please ask if you need more information. Cheers, David
