On Sun, Mar 10, 2013 at 10:31:08PM -0700, Michael Johnson - MJ wrote: > I currently have a btrfs filesystem that I am unmounting and it has > been has been "unmounting" for the last 20 minutes. > > I'm pretty sure I know exactly what is going on and in my current > situation it's not a huge issues, but it would be a problem if this > was a production system and I was trying to do a maintenance. > > Here is how I got into this situation: > > I am migrating my data from one pair of disks (mirrored with btrfs) to > another pair of disks. I rsync'd my data from the original btrfs file > system to the other. When it completed, my new filesystem showed > 165GB used. The original show 1.8TB used. I came to the conclusion > that it must be the daily snapshots I have that were using the > majority of the space and because I was going to destroy the > filesystem, I decided, what the heck, let me destroy the snapshots and > see what it looks like. > > To my surprise, removing all the snapshots resulted in the usage > dropping from 1.8TB to 1.7TB. I re-ran my rsync, it complete without > transferring any new data. I then did a du -s in the mountpoint for > the original filesystem and is reported back 165GB which agrees with > what rsync and df on the new filesystem reports. > > My first thought was that I must have some sort of bizarre corruption > on the original filesystem. And then I went to unmount it and it > still has not returned. > > What I now suspect is going on is that while deleting the snapshots > was quick, that probably kicks of a background thread which actually > does the heavy lifting. I noticed a btrfs-cleaner process that was in > an io wait state, which I presumed was the process in question. > However, now 40 minutes later, my unmount is still hung and the > btrfs-cleaner process is sleeping, so perhaps I am wrong.
You're right, umount will wake up cleaner kthread to do 'real work' of cleanup marked 'delete' snapshot/subvolume. but while btrfs-cleaner is sleeping, could you please show what unmount is waiting for? Maybe 'cat /proc/xxxx/stack' will be helpful on figuring out why. thanks, liubo > > At this point I am going to powercycle my system, but I figured I > would check and see if anyone else knew for certain it this was the > type of behavior one would expect to see when removing large snapshots > and then immediately trying to unmount the filesystem. If so, it > seems like this is something that would need to change before someone > would want to seriously consider using btrfs w/ snapshots in a > production environment. I know btrfs is not considered production > ready yet (well, at least not by the developers, regardless of what > Oracle and Suse say). At the same time, I've not been able to find > any mention of similar problems, so I figured it was worth mentioning. > > -- > Michael Johnson - MJ > -- > 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 -- 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
