Bug#608532: linux-2.6: very low I/O performance when vm's virtual disk placed on btrfs partition

[Aron Xu <happyaron.xu@gmail.com>]

Package: linux-2.6
Version: 2.6.32-29

While I was running a qemu-kvm virtual machine, I placed the virtual
disk on one of my btrfs partition and it results in very low I/O
performance. Comparing with an Ext3/4 host partition, it slows several
times.

The test I ran was installing Squeeze using d-i beta2 netinst ISO
image, using expert installation mode:

1. The one using btrfs got nearly stopped at approximately 33% (it's
the time to start installing base system, i.e. installing
apt/aptitude). It takes about 1 hour to go forward to 50%, with my
hard disk making a lot of noise, and finally I shut down the virtual
machine.

2. The other one using ext4, which I tried to compare the performance,
can finish the installation in ~45 minutes.

The two partition are exactly the same hard disk, actually I formatted
the previous btrfs partition to ext4 when I ran the test.

-- 
Regards,
Aron Xu