On Fri, May 25, 2012 at 10:27 PM, Peter Maloney <peter.maloney@xxxxxxxxxxxxxxxxxxxx> wrote: > On 05/25/2012 09:10 PM, Alexander Block wrote: >> Just to show some numbers I made a simple test on a fresh btrfs fs. I >> copied my hosts /usr (4 gig) folder to that fs and checked metadata >> usage with "btrfs fi df /mnt", which was around 300m. Then I created >> 10 snapshots and checked metadata usage again, which didn't change >> much. Then I run "grep foobar /mnt -R" to update all files atime. >> After this was finished, metadata usage was 2.59 gig. So I lost 2.2 >> gig just because I searched for something. If someone already has >> nearly no space left, he probably won't be able to move some data to >> another disk, as he may get ENOSPC while copying the data. >> >> Here is the output of the final "btrfs fi df": >> >> # btrfs fi df /mnt >> Data: total=6.01GB, used=4.19GB >> System, DUP: total=8.00MB, used=4.00KB >> System: total=4.00MB, used=0.00 >> Metadata, DUP: total=3.25GB, used=2.59GB >> Metadata: total=8.00MB, used=0.00 >> >> I don't know much about other filesystems that support snapshots, but >> I have the feeling that most of them would have the same problem. Also >> all other filesystems in combination with LVM snapshots may cause >> problems (I'm not very familiar with LVM). Filesystem image formats, >> like qcow, vmdk, vbox and so on may also have problems with atime. >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html > Did you run the recursive grep after each snapshot (which I would expect > would result in 11 times as many metadata blocks, max 3.3 GB), or just > once after all 10 snapshots (which I think would mean only 2x as many > metadata blocks, max 600 MB)? > I've run it only once after creating all snapshots. My expectation is that in both cases the result is the same. If all snapshots have the file /foo/bar, then each individual snapshotted copy of it would have a different atime and thus an own metadata block for it. As this happens with all files, no matter how i iterated the files, then nearly all metadata blocks get their own copy. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
