Bug#576673: closed by Bastian Blank <waldi at debian.org> (Re: Bug#576673: lvm2: unmount lvm snapshot takes a long time - high disk I/O)

[James Robertson]

I realise this bug is closed but I have discovered how to resolve this
problem and i'm replying here for the benefit of anyone who is
researching the same problem.

I found that if I mounted the snapshot read only e.g. "mount -o ro
/dev/vg00/home-snapshot /mnt/home-snapshot" I did not encounter the
disk activity and lenghty unmount delay.

I also tested this using a Debian Kernel (2.6.32-4-amd64) and got the
same behaviour and the delay appears proportionate to the amount of
data copied from the snapshot (in my case a fairly large rsync) as
when I simply mounted and unmounted it was instantaneous and a small
copy job caused a small delay and disk activity.

Thanks and Regards,

James