Nick Guenther wrote: >>>> So, as nicely summarized at >>>> > http://www.h-online.com/open/news/item/Possible-data-loss-in-Ext4-740467.html > , >>>> ext4 is kind of broken. It won't honor fsync and, as a /feature/, will >>>> wait up to two minutes to write out data, leading to lots of files >>>> emptied to the great bitbucket in the sky if the machine goes down in >>>> that period. >> There is a very simple explanation for why things are so. >> Actual data file loss has never been what these things were coded for. >> filesystem *tree and meta-data*, ie. the structure of how things are >> knit together, is the main concern. If you lose the filesystem tree >> structure, you've lost all your files, not just the newest ones. >> Therefore the goal is safe metadata handling. The result is you can >> lose specific data in specific (newly written to) files, but the >> structure of the filesystem is consistant enough for fsck to not damage >> it.
> See, since it seems that BSD doesn't have this file-data consistency > guarantee, are Linus' worries about ext4's potential data loss just > being alarmist? It seems to me that the case described in > https://bugs.edge.launchpad.net/ubuntu/+source/linux/+bug/317781/comments/45 > is just as likely to happen on OpenBSD--if I run KDE or GNOME and mess > around with my settings then quickly murder the system the files will > be resurrected empty, right? It seems like some posters in this thread somehow misses the fact that if you have outstanding writes and the box dies. Some of your data dies also. New or old data, something will be missing. >From the point your app does a write(), it gets buffered in the I/O handling, it gets buffered by the device driver for the card, it gets buffered in the card probably, it gets buffered on the on-disk memory cache and then it serially hits the platter one bit a a time until its all written. If you have data in this long pipe and the power goes, you will lose data, period. OpenBSD has chosen to try harder to keep the metadata intact, and ext4 doesn't try at all, for the love of speed. Still, you are only moving around the window of opportunity for fail, and sometimes making it larger or smaller, but it is always there. The last comment above should really only read: "If I quickly murder my system, the files might be gone". Nothing else. If you have writes going, data loss is a reality. Sometimes more, sometimes less, but its all games with statistics. If ext4 has a 50% chance of killing your files and FFS on obsd has 1%, you might still get to keep your KDE settings on either system or you may lose them all. It shouldn't be news to anyone that Linux always went for fast-and-insecure whereas the BSDs opted for slower-but-safer for the filesystems. Making a fuss about how insecure the penguins are this week feels like a waste of time to me. If you care about your data, you have backups. Regardless of if the probability is 1% or 50%, because for someone out there, the percentages will be against you.
