Destination file a lot larger then source (real size)

[milos.kaurin at gmail.com]

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 <ms at citd.de> wrote:

> On 05.02.2013 12:32, milos.kaurin at 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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