You are spot-on! After clearing the non-dirty cache I get the correct filesize with du -hs
I will add the fstab option you suggested to my NFS server's fstab Thank you! On Tue, Feb 5, 2013 at 1:04 PM, Matthias Schniedermeyer <m...@citd.de> wrote: > On 05.02.2013 12:32, milos.kau...@gmail.com wrote: > > I have a script that syncs my backups to an NFS mount every day > > > > The script works fine, without any errors, but there is a problem when > > it comes to some large files > > > > Let's take my pst file (8.9 gig) as an example > > > > Source: > > > > du -hs mypst.pst > > 8.9G mypst.pst > > ls -alh mypst.pst > > -rw-rw---- 1 me me 8.9G Jan 25 17:07 mypst.pst > > > > That seems OK > > > > > > Let's do that on the destination: > > > > du -hs mypst.pst > > 17G mypst.pst > > ls -alh mypst.pst > > -rw-rw---- 1 root root 8.9G Jan 25 17:07 mypst.pst # Permissions here > are > > fine, disregard > > > > > > Real file size is almost double size! > > > > > > Extra info: > > > > Source dir is an xfs partition > > The NFS mount is also xfs on the NFS server > > NFSv4 > > > > Full cmdline for the daily backup: > > /usr/bin/rsync -rltgoD --no-perms --no-owner --no-group --delete <src> > > <dest> > > > > For the testing purposes, I've tried doing: > > rsync /srcdir/mypst.pst /nfsmount/mypst.pst > > and the result is the same: du reports 17 gigs, and ls -alh reports 8.9 > > > > Is there any way around this? > > This is a feature of XFS called "speculative preallocation". If you > open/append/close a file repeatetly XFS preallocates space in > anticipation of more appends, the feature helps to prevent or at least > reduce fragmentation. > > You can see the extents of a file with xfs_bmap. > > You can get rid of the preallocation in several ways: > - Trash your buffer-cache with unreleated things > (The prellocation gets dropped when the inode of the file is evicted > from cache) > - umount/mount cycle > - Drop whole cache, as root: > echo 3 > /proc/sys/vm/drop_caches > This drops the whole non-dirty cache of Linux! > > There was talk on the maillinglist to drop preallocations after some > time (like 5 minutes), but AFAIR there weren't patches. So IFF that is > implemented that means kernel 3.9 or later at the earliest. > > If you don't want speculative preallocation you can disable it with the > mount-option allocsize. e.g. "allocsize=4k" > > > > > -- > > Matthias >
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