Janne Johansson wrote: > 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. >
I know this is a bit off topic, but storage devices have battery's on RAID cards for a reason. If you are worried about read/writes etc when a system dies, there are measures you can take
