Re: [linux-lvm] Help, lvm2 snapshot and XFS , using xfs_freeze to do this, but then lvcreate hang.

[Steve Feehan <sfeehan@boolecat.com>]

On Tue, Sep 26, 2006 at 10:32:51PM -0700, David Brown wrote:
> bowen zheng wrote:
> 
> > Help, lvm2 snapshot and XFS , using xfs_freeze to do this, but then
> > lvcreate hang.
> 
> The lvcreate does the xfs_freeze for you, so if you run xfs_freeze, then
> the lcreate will hang.  Running it with '-u' should allow the lvcreate to
> hang.

Are you saying that the lvcreate command literally executes xfs_freeze
when used on a volume that happens to contain an XFS filesystem? Or
that creating a snapshot is equivalent to using xfs_freeze?

I too had read that it was suggested to call xfs_freeze before creating
a snapshot. This worked on a Debian system a year or two ago. And then
it stopped. I'm not sure if it was a kernel, lvm2 or xfs utilities
update that caused it to stop working. I did file a debian bug a while
back but nothing ever came of it:

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=285979

> > I use lvm2 and xfs both.  If I do not use xfs_freeze before, I can use
> > lvcreate snapshot the lv. And it work fine for some static files or
> > lv, but not for running system such as / (root) which will generate a
> > log of I/O error.
> 
> What kind of errors are you getting.  I've done this on active filesystems
> for backup purposes, and not had any problems.

Running xfsdump on the snapshot I see many warnings like:

debug: starting dump at Wed Sep 27 06:00:02 EDT 2006 ...
/sbin/xfsdump: WARNING: failed to get bulkstat information for inode 3692873
/sbin/xfsdump: WARNING: failed to get bulkstat information for inode 3692876
/sbin/xfsdump: WARNING: failed to get bulkstat information for inode 3692873
/sbin/xfsdump: WARNING: failed to get bulkstat information for inode 3692876
/sbin/xfsdump: WARNING: could not stat dirent vg0_04875.vg ino 3692872: No such file or directory
/sbin/xfsdump: WARNING: could not stat dirent vg0_04876.vg ino 3692875: No such file or directory
/sbin/xfsdump: WARNING: failed to get bulkstat information for inode 3692873
/sbin/xfsdump: WARNING: failed to get bulkstat information for inode 3692876
/sbin/xfsdump: WARNING: could not stat dirent vg0_04875.vg ino 3692872: No such file or directory: using null generation count in directory entry
/sbin/xfsdump: WARNING: could not stat dirent vg0_04876.vg ino 3692875: No such file or directory: using null generation count in directory entry
/sbin/xfsdump: WARNING: failed to get bulkstat information for inode 3692873
/sbin/xfsdump: WARNING: failed to get bulkstat information for inode 3692876
/sbin/xfsdump: WARNING: failed to get bulkstat information for inode 3692873
/sbin/xfsdump: WARNING: failed to get bulkstat information for inode 3692876
debug: dump complete at Wed Sep 27 06:00:04 EDT 2006 ...

-- 
Steve Feehan