On Thu, 2007-08-02 at 00:09 +1000, David Chinner wrote: > [lvm snapshot] hangs on a lock that is held across the xfs_freeze -f ; > xfs_freeze -u sequence. Right. > > I suppose > > how to fix this is a question for the linux-lvm mailing list. > > IIRC from the last time this came, they'll tell you not to use > xfs_freeze. Well, two problems with that: 1. There is no way to atomically create snapshots of two different volumes (the main filesystem and the log) without using xfs_freeze. 2. I tried without xfs_freeze anyway just to see what would happen, and actually in kernel 2.6.22.1 if you simply create a snapshot of the main filesystem volume and destroy it several times in a row (not even touching the log volume yet) lvcreate hangs. So it sounds like there is a fundamental problem with the approach, plus a bug somewhere... I will copy this to linux-lvm. For the benefit of those reading on linux-lvm, the issue is that I am trying to snapshot an XFS filesystem with an external log. To do this it is necessary to snapshot two volumes--the main filesystem volume and the log volume--while the filesystem is frozen. It is not sufficient to freeze the filesystem separately for each snapshot creation since its state might change between the two snapshots. The correct approach is to use xfs_freeze to freeze the filesystem, then create both snapshots, then unfreeze it. This used to work 100% reliably with kernel 2.6.16, device-mapper 1.02.03 and LVM2 2.02.02. With device-mapper 1.02.21 and LVM2 2.02.27, lvcreate hangs while creating a snapshot of a filesystem that has been frozen with xfs_freeze. Furthermore, when using kernel 2.6.22.1 (and latest device-mapper and LVM2), even if I do not use xfs_freeze, lvcreate hangs about 10% of the time when creating a snapshot. Once in the hung state (whether because xfs_freeze was used or because of the random hang) it seems impossible to get it unstuck without rebooting the system. I guess this is not an XFS-specific problem--it would happen with any filesystem employing a separate log volume. I am happy to test any patches that might address this issue... or maybe even hack one up myself if someone gives me some pointers, but I guess someone who knows something about LVM should really do it. -- Mario Becroft <mb@gem.win.co.nz> _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
