On Fri, Apr 28, 2017 at 3:10 AM, Christophe de Dinechin <dinec...@redhat.com> wrote:
> > QEMU qcow2. Host is BTRFS. Guests are BTRFS, LVM, Ext4, NTFS (winXP and > win10) and HFS+ (macOS Sierra). I think I had 7 VMs installed, planned to > restore another 8 from backups before my previous disk crash. I usually have > at least 2 running, often as many as 5 (fedora, ubuntu, winXP, win10, macOS) > to cover my software testing needs. That is quite a torture test for any file system but more so Btrfs. How are the qcow2 files being created? What's the qemu-img create command? In particular i'm wondering if these qcow2 files are cow or nocow; if they're compressed by Btrfs; and how many fragments they have with filefrag. When I was using qcow2 for backing I used qemu-img create -f qcow2 -o preallocation=falloc,nocow=on,lazy_refcounts=on But then later I started using fallocated raw files with chattr +C applied. And these days I'm just using LVM thin volumes. The journaled file systems in a guest cause a ton of backing file fragmentation unless nocow is used on Btrfs. I've seen hundreds of thousands of extents for a single backing file for a Windows guest. -- Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
