fugazzi® posted on Thu, 31 Dec 2015 09:01:51 +0000 as excerpted: > Just one question for the gurus here. > > I was wondering: if I disable write barriers in btrfs with the mount > option nobarrier I just disable the periodic flushes of the hardware > disk cache or I'm disabling also the order of the writes directed to the > hard disk? > > What I mean is: is it safe to disable write barrier with a UPS with > which I will likely have the hardware always powered even in the event > of a kernel crash, freeze, etc? > > I'm asking because if also the ordering of the write is no more > guaranteed I guess it would not be safe to disable write barrier even if > the possibility of an unexpected power down of the HD was remote because > in the case of a crash the order of the write would be messed up anyway > and we could boot up with a completely corrupted fs. >From the wiki mount options page: https://btrfs.wiki.kernel.org/index.php/Mount_options >>>>> nobarrier Do not use device barriers. NOTE: Using this option greatly increases the chances of you experiencing data corruption during a system crash or a power failure. This means full file-system corruption, and not just losing or corrupting data that was being written during the event. <<<<< IOW, use at your own risk. In theory you should be fine if you *NEVER* have a system crash (it's not just loss of power!), but as btrfs itself is still "stabilizING, not yet fully stable and mature", it can itself crash the system occasionally, and while that's normally OK as the atomic transaction nature of btrfs and the fact that it crashes or at minimum forces itself to read-only if it thinks something's wrong will normally save the filesystem from too much damage, if it happens to get into that state with nobarrier set, then all bets are off, because the normally atomic transactions that would either all be there or not be there at all are no onger atomic, and who knows /what/ sort of state you'll be in when you reboot. So while it's there for the foolish, and perhaps the slightly less foolish once the filesystem fully stabilizes and matures, right now, you really /are/ playing Russian roulette with your data if you turn it on. I'd personally recommend staying about as far away from it as you do the uninsulated live service mains coming into your building... on the SUPPLY side of the voltage stepdown transformer! And for those that don't do that, well, there's Darwin awards. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
