I was working on a document in LibreOffice today while my battery was low and so I was frequently saving, which I thought would help me if I lost power. However, when I eventually did lose power and later rebooted, the document had become 0 bytes long. LibreOffice was not able to restore the auto-saved copy either. As a result, I have lost a whole week of notes for one of my courses.
After researching online, it seems that this is caused by the application not calling fsync() (or fdatasync()) when saving files. Due to delayed allocation in modern filesystems, there is no guarantee that the new file's data has actually been written to disk unless the application calls fsync. So if an app writes a new file and replaces the old one with it without fsync'ing the new one first then there is a window of opportunity during which a power failure will result in the loss of BOTH versions of the file. In ext4 this window is also much larger than in ext3.
Theodore Tso blogged about this at http://ldn.linuxfoundation.org/blog-entry/delayed-allocation-and-zero-length-file-problem and http://www.linuxfoundation.org/news-media/blogs/browse/2009/03/don%E2%80%99t-fear-fsync. He strongly recommends to call fsync in this situation.
Please update LibreOffice to fsync() saved files so that other users do not lose their data like I did.
DistroRelease: Ubuntu 11.04
Package: libreoffice-core 1:3.3.2-1ubuntu5
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 22.214.171.124
Uname: Linux 2.6.38-8-generic x86_64
Date: Wed Jul 27 21:37:02 2011
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release amd64 (20100429)
UpgradeStatus: Upgraded to natty on 2011-04-29 (89 days ago)